A Guide to Image Optimisation

Images can transform your emails, drive engagement, and energise your content. They are a great tool for all email marketers. 

But, they can also impact accessibility, loading time, and mobile optimisation, which can cause readers to give up on an email. Optimising images, therefore, improves deliverability and engagement.

Here are some top tips to help you with image optimisation.

Image Size⚡️ #

• Images should be between 600-1000 px wide
• They should be less than 2000 px high
• You can edit sizing under the Styles tab on Klaviyo

File Size⚡️ #

• The ideal file size is under 1MB
• It can go up to 5MB (on Klaviyo)
• You can compress files using online tools

File Format⚡️ #

• Klaviyo Supports PNG, JPG, and GIF
  • PNG
    • Works for all images, no need for compression
    • Especially suited to images with text in them
    • Can have slower loading times
  • JPG
    • For photographs only
    • Fast-loading
    • Doesn’t work when images contain text because they compress when they’re uploaded
  • GIF
    • Perfect for logos and animations
    • Small file size
    • They don’t compress when uploaded
    • But they can be quite grainy
  • NOTE: You don’t have to commit to only one file format forever. Think about what will enrich this particular email.

Clickable Pictures⚡️ #

• Use your pictures as part of your Call-to-Action
• Incorporate links and actions into the pictures to improve Click-Through Rates

Mobile Optimisation⚡️ #

• Nearly 50% of emails are opened on mobiles rather than desktop devices
• Choose email templates which are responsive to the device they are opened on
• Under the Styles tab on Klaviyo, toggle ‘Optimise for Mobile’ to ‘On’ where possible

ALT-Text⚡️ #

• This is not a caption. It’s a description of the image. 
• It helps visually impaired readers, but also supports Search Engine Optimisation (SEO) and keyword filters

⚠️Never rely solely on images⚠️ #

Images enrich your emails. They look pretty and keep things fresh and exciting. 

But they should never replace text. Here’s why:

1. They are more unreliable than text – Images can load slowly or not at all. If you only use images, and something goes wrong, readers lose the message of your email. Similarly, those who have turned off images in their inbox won’t benefit from the email.
2. Spam Filters are more likely to flag them – Spam emails are often image heavy, to try to bypass text filters. This means spam filters flag emails with high-image content. 
3. They are not accessible –  Voice-recognition equipment cannot pick up on images. You risk cutting out a large number of your potential market. 

You should aim for a ratio of 80:20 – more text than image. 

⚡️Remember to run tests #

See if your images are working as you’d planned, by running A/B tests and sending out trial emails. Test out your images on both mobile and desktop devices, and keep an eye on loading time, quality, and accessibility. 

⚡️See the bigger picture #

For more help with your email campaigns, check out our articles on

3. How to improve email deliverability
4. Alt-text

Plus, if you want help really zooming in on the details, we’re around! Contact Zap today, and a member of our expert team can help you get the most out of your campaigns.