I have set the flags for my language selectors to use base-encoding, so the source is something like this:

data:image/gif;base64,R0lGODdhEgAMAPEAACFGi////64cKAAAACwAAAAAEgAMAAACF5SPqcvtr4KctNqLs94W+A+G4kiW5ikWADs=

Now I would like to exclude those from the image sitemaps. I tried this by simply taking a part of the string that is identical for both these images ( R0lGOD ) and set that in the exclude filter for the image XML-sitemap, however, it is not being accepted.
Do you know if this is possible?

Yes that's possible but take it easy, just use a 'base64' string in the exclude filters.

Just add the 'base64' comma separated for ALL data sources involved in the images sitemap generation and clear ALL cache to ensure to refresh the images sitemap excluding all images having the string 'base64' in the path like this: data:image/gif;base64,R0lGODdhEgAMAPEAACFGi////64cKAAAACwAAAAAEgAMAAACF5SPqcvtr4KctNqLs94W+A+G4kiW5ikWADs=

Regards

Perfect! Thanks for the quick response again