About Images in Blogger

Image Subtitle (Medium Size)

Search engines like Google uses images larger than 1200px in width or height, example the image usage in Google Discover.

We also know that Fb uses 1200px in image width for best Post image display.

In another words, try to upload images larger than 1200px but compress them first before you upload, so the image file size is lighter. The image resolution may deteriorate, but slightly un-noticable.

For your info, uploading via Blogger UI does not count to your Google Account storage space. Earlier the max image file size is 2048px, before the image files is counted. So keep in this image sizes safe zone, as we do not know what changes will happen next... 

There is unlimited storage for uploaded images just as long you upload below 2048px in width and/or height.

More info: https://support.google.com/blogger/answer/41641?hl=en&ref_topic=3339243

Meaning, it is still free and you can uploads thousands more as long as your images size is not larger than explained earlier.

Images larger than 2048px will be counted with the Google Account storage space of the uploader. This you need to check at your Accounts > Storage dashboard.