How to enable image renditions on SharePoint 2019
When you install SharePoint onprimises the image renditions are not generated automatically, and the renditions pages displays the error message below.
The blob cache is not enabled in this web application. Image renditions will not be generated until the blob cache is enabled. For information on turning on the blob cache, please review the product documentation.
To fix this issue and get the image renditions automatically generated follow the instructions provided in this article.