Email Image Best Practices: The Complete Guide for Marketers

Images can make or break your email campaigns. When used effectively, they capture attention, reinforce your message, and drive engagement. When implemented poorly, they can hurt deliverability, slow loading times, and create accessibility issues. This guide covers everything marketers need to know about using images in email campaigns effectively.

Image Selection: Purpose Before Aesthetics

Every image in your email should serve a clear purpose:

Relevance to Message

Choose images that reinforce or clarify your message rather than simply decorating the email. Ask yourself: “Does this image help communicate our key point?”

Best practice: Before adding an image, define its specific purpose in the email. Is it showing product details? Creating emotional connection? Directing visual flow? If you can’t articulate its purpose, reconsider using it.

Brand Consistency

Your email images should align with your overall visual brand identity. Inconsistent visual styles create a disjointed experience that weakens brand recognition.

Implementation tip: Create an email-specific style guide that defines image styles, treatments, and usage guidelines aligned with your broader brand standards but optimized for email environments.

Technical Specifications

File Formats

Different image types serve different purposes in email:

  • JPG - Best for photographs and complex images with many colors
  • PNG - Ideal for images requiring transparency or with text/line art elements
  • GIF - Use for simple animations (but use sparingly)
  • SVG - Supported in some clients for lightweight, scalable icons (but always have fallbacks)

Best practice: Use JPGs for most photo content and PNGs for graphics with text or transparency needs. Convert detailed illustrations to JPG when possible to reduce file size.

File Size Optimization

Large images significantly impact load times and can trigger spam filters.

Guidelines:

  • Keep individual images under 200KB (ideally under 100KB)
  • Keep total email weight under 150KB (preferably under 100KB)
  • Resize images to the exact dimensions needed before adding to email

Implementation tip: Use tools like TinyPNG, ImageOptim, or Squoosh to compress images without noticeable quality loss.

Dimensions and Resolution

Email images should be sized appropriately for their display context:

  • Hero images: 600-650px wide (standard email container width)
  • Product images: 320-600px wide depending on layout
  • Logos and icons: Keep under 200px in either dimension when possible

Best practice: Design for 2x display density (Retina) but compress effectively. For example, a full-width email image might be created at 1200px wide but displayed at 600px wide using HTML attributes.

Email Client Considerations

Image Blocking

Many email clients block images by default. Your emails must remain functional and comprehensible even with images disabled.

Implementation checklist:

  • Use descriptive ALT text for all images
  • Never put critical information only in images
  • Design with “images off” view in mind
  • Avoid image-only emails entirely

Real-world example: Notice how brands like Slack and GitHub design emails that remain perfectly usable with images disabled, using HTML text for all critical information.

Rendering Differences

Email clients display images differently:

  • Outlook often adds unwanted spacing around images
  • Gmail may clip messages over 102KB, hiding images at the bottom
  • Dark mode can invert image colors unexpectedly

Best practice: Use table cell padding of 0 and set images to display:block to prevent unwanted gaps. Test emails in dark mode to ensure images remain legible.

Layout and Design Best Practices

Text-to-Image Ratio

Emails with too many images and too little text are more likely to trigger spam filters.

Guideline: Maintain at least a 60:40 ratio of text to images. Never send an email that’s one large image or primarily images.

Image Placement

Strategic image placement impacts engagement:

  • Hero images should be immediately visible without scrolling
  • Product images benefit from consistent sizing and placement
  • Decorative elements should guide attention, not distract from CTAs

Best practice: Use the inverted pyramid approach—lead with a compelling hero image, follow with supporting visuals, and ensure images direct attention toward your call to action.

Responsive Considerations

Images must work across device sizes:

Implementation technique:

<img src="image.jpg" alt="Description" style="width: 100%; max-width: 600px; height: auto;" width="600">

This approach ensures images resize proportionally on small screens while not exceeding their natural size on larger displays.

Accessibility Requirements

Alternative Text

ALT text is essential for:

  • Screen reader users
  • Subscribers with images disabled
  • Providing context when images fail to load

Best practice: Write ALT text that concisely describes the image content and its purpose. For decorative images, use empty ALT text (alt="") rather than omitting the attribute.

Examples:

  • Poor: alt="image1"
  • Better: alt="Woman using laptop outdoors"
  • Best: alt="Remote worker accessing email platform on mountain retreat"

Text in Images

Avoid putting critical text in images whenever possible. When necessary:

  • Ensure high contrast for readability
  • Use ALT text that includes the exact text from the image
  • Keep font sizes large enough to be legible on mobile

Advanced Image Techniques

Background Images

Background images can create visually rich layouts but require careful implementation:

<!-- VML for Outlook -->
<!--[if gte mso 9]>
<v:image src="background.jpg" style="width:600px;height:400px;"/>
<v:rect fill="false" stroke="false" style="position:absolute;width:600px;height:400px;">
<v:textbox inset="0,0,0,0">
<![endif]-->

<!-- Standard approach -->
<div style="background-image: url('background.jpg'); background-size: cover; background-position: center; width: 100%; max-width: 600px; height: 400px;">
  <!-- Content here -->
</div>

<!--[if gte mso 9]>
</v:textbox>
</v:rect>
<![endif]-->

Best practice: Always include a fallback background color that provides sufficient contrast for text if the image fails to load.

Animated GIFs

Used strategically, animated GIFs can increase engagement:

Guidelines:

  • Keep file size under 150KB (preferably under 100KB)
  • Limit to 3-5 frames for better performance
  • Put the most important content in the first frame (Outlook only shows the first frame)
  • Don’t rely on animation for critical information

Implementation tip: Use tools like EZGif to optimize animated GIFs by reducing colors, frames, and dimensions.

Image Slicing

For complex layouts, slicing large images into smaller pieces provides more layout control:

Best practice: When slicing images:

  • Maintain consistent file naming (e.g., header_01.jpg, header_02.jpg)
  • Use table structures with cellpadding and cellspacing set to 0
  • Ensure pieces align perfectly to avoid visible seams

Image Hosting and Delivery

Reliable Hosting

Images should be hosted on reliable, fast servers dedicated to email content.

Best practice: Host email images on:

  • Your ESP’s image hosting service
  • Content delivery networks (CDNs)
  • Dedicated image hosting services

Avoid hosting on your main website server, which could slow down if an email campaign drives significant traffic.

Tracking Considerations

Many ESPs add tracking codes to images, which can affect loading times.

Best practice: Be aware of which images contain tracking pixels and prioritize the loading of critical visual content by placing tracked images lower in your email when possible.

Testing and Optimization

A/B Testing Images

Systematically test image variables including:

  • Image vs. no image
  • Product-only vs. product-in-use
  • Lifestyle vs. studio photography
  • Various emotional appeals

Implementation tip: Test one variable at a time with meaningful sample sizes (at least 1,000 recipients per variant) to get actionable data.

Image Load Time

Monitor image load times as part of your email testing process. Slow-loading images significantly impact engagement rates.

Best practice: Use email testing tools like Litmus or Email on Acid to check load times across different connection speeds.

Implementation Checklist

Before sending any email campaign, verify these image best practices:

  • All images have descriptive ALT text
  • Images are compressed and optimized for fast loading
  • Email remains functional with images disabled
  • Images are responsive and display correctly on mobile devices
  • No critical information exists only in images
  • Total email size is under 1MB (ideally under 500KB)
  • Text-to-image ratio is at least 60:40
  • Image paths are absolute (not relative)
  • Images are hosted on reliable servers
  • Dark mode appearance has been tested

Conclusion

Email images require balancing technical constraints with creative objectives. By following these best practices, you’ll create emails that load quickly, display consistently across clients, remain accessible to all users, and most importantly, effectively communicate your message and drive conversions.

Remember that the best email images aren’t just visually appealing—they’re purposeful, optimized, and implemented with both user experience and technical constraints in mind.