Get nicer thumbnails for my Post snippets

I recently received some feedback that my thumbnails are a bit nicer than the standard thumbnails offered by Blogger. This is because I use a custom snippet in my Blog widget, to produce bigger thumbnails, using the new resizeImage operator.

Note: This post leverages the techniques described in the article about Responsive images for Google photos.

A note:

The resizing behaviour provided on Blogger requires that the image is hosted on a Google platform to work - provided that you add your images by uploading them in the editor, this technique should work.

Creating a responsive, resized Thumbnail

The resize operator takes 3 parameters - the URL of the image, the width to resize it to, and an optional ratio for a cropped version of the image.

<img expr:src=’resizeImage(data:post.firstImageUrl, 300)’ />

In my Blog widget, I've customized the HTML so that on feed views (homepage, search, etc), I display post snippets instead of the full post. As a part of these snippets, I do a square-cropped responsive image. sourceSet is the srcset counterpart of the function for resizing an image.

<img expr:src='data:post.firstImageUrl'
     expr:srcset='sourceSet(data:post.firstImageUrl, [32, 64, 128], "1:1")'
     sizes='(max-width: 800px) 12vw, 128px' />

If you're not sure what's going on here, the breakdown by attribute is:
  • src: The image source fallback, for browsers with no responsive support. The first image in the post.
  • srcset: A set of (Image URL, Width) pairs, that tells the browser which URL to pick when the image is a given size.
  • sizes: A hint for the browser what sizes the image will be displayed at. My thumbnail's CSS is 12% of the viewport width for small screens, and 128x128 on larger screens.

Applying it to your Blog

  1. Head to
  2. (Select your blog)
  3. Hit 'Template'
  4. Hit 'Edit HTML'
  5. Hit 'Jump to Widget', select 'Blog1'
  6. Find the b:includable with the id 'post'
Once in that includable, you'll need to add a branch for whether it's a feed page or an item page.

<b:if cond='data:blog.pageType not in {"static_page","item"}'>
  <!-- Responsive image, and snippet -->
<b:else />
  <!-- The stuff that's already there. -->

Happy thumbnailing!


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