Blurry images on blogger is a common issue with new blogger UI. As we know that blogger UI is migrated to a new user interface. So, critical issues are expected, especially if you’re not using the default blogger themes. We can fix the blogger blurry images with some tweaks in your theme HTML file.
Many users reported that image thumbnails or featured images are blurry in new blogger. A user reported on the blogger community. “This problem is coming to a new blogger. when I upload images through old bloggers, they saw perfectly.”
Reason For Blurry Images on Blogger
You will most likely face blurry images or blurry thumbnails on the blogger homepage if you’re using a custom or third-party theme. This means you will not face this problem if you have the blogger’s default theme.

The new blogger UI outputs the images URL as /w640-h426/ while if you are using a custom theme or a 3rd party theme then it will look something like this /s640/. This image URL format is responsible for image resizing. So, if the image URL format is not correct and aligned with the new blogger image URL format, then this issue will occur.
A quick solution is to replace s72-c with s72-c-k-no. You can search for s72-c inside your blogger theme HTML file. But if your custom or 3rd party theme is encrypted then you will not find it untill you decode the HTML code.
How to Fix Blurry Images or Thumbnails on Blogger
We can fix blogger blurry images with some tweaks in your theme HTML file. But first, figure out what exactly the reason is? First, backup your template and then apply the blogger default theme. This should resolve your issue. Also, this means you have a problem with your 3rd party template. Follow these steps to troubleshoot this critical issue.
Note: If you can not find the script then contact your theme developer. Or you can hire a Blogger Expert.
Step 1. Backup your theme.
Step 2. Search for the following script inside your theme HMTL file.
<data:post.thumbnailUrl />
or
data:post.thumbnailUrl
Step 3. Replace the above script with the following script given below.
<b:eval expr='resizeImage(data:post.thumbnailUrl, 200, "1:1")' />
Step 4. Save the theme.
The new Blogger UI has replaced the old Blogger user interface. Although there is an option to revert to the legacy interface. But this option will not be available after August 24. 2020. The new Blogger UI has many new and updated features. With the constantly growing web, it is a significant decision to introduce fresh and improved design.
Blogger became responsive, both on desktop and mobile. Everything including posts, comments, stats, editors, reading lists, and settings got a fresh look. Blogger’s new UI became default UI for everyone. But if you want to revert to the old user interface, then you can click “Revert to legacy Blogger”. Similarly, if you still did not try the new UI, you can click “Try the New Blogger”.