In Sitefinity Build 7.2.5320.0 (Hotfix2) we introduced a change to the thumbnails  hash algorithm by switching it from MD5 to SHA1. This breaks the thumbnails in cases where  custom crop size is used and EnableImageUrlSignatureTitle is set to true in the configurations.

When upgrading from version lower than 7.2 Hotfix 2, the hash algorithm will be set to the old format MD5 and the thumbnails will be resolved properly.

New installations of 7.2 and later will use the SHA1 algorithm.

In Sitefinity Build 7.2.5320.0 (Hotfix2) we introduced a change to the thumbnails  hash algorithm by switching it from MD5 to SHA1.

From internal build 7.3.5613 configuration for the hash algorithms is supported.  Switching between them is done through the backend configurations(Settings -> Advanced -> Libraries -> Images -> Image URL Signature hash algorithm)  or by editing the LibrariesConfig.config ( App_Data/Sitefinity/Configuration).

If Images are generated with one of the hash format and then the algorithm is switched the thumbnails will be broken. In this case,  recreate your thumbnails or set enableMultipleHashAlgorithmsSupport =”true” that will check if the hash is valid for both algorithms SHA1 and MD5.

There is option to use both the algorithms in case of thumbnails generated between 7.2 Hotfix 2 and 7.3 release.

The option is not visible in the UI and can be applied  only through LibrariesConfig.config ( App_Data/Sitefinity/Configuration) by setting enableMultipleHashAlgorithmsSupport  =”true”

In this case the thumbnails do not need to be recreated.