I don't get the 'delete image' option from album toolbox since upgrading to 1.4.2.2 from the version just after the really scarey ajax plugin vulnerability.

I'm using zpMinimal theme, however in Default the 'delete image' option is absent, too.

I couldn't find a changelog on the Trac website.

I don't remember any change but I see it is missing. My colleague sbillard will know more.

All "editing" functions are removed from the front end pages (e.g. the Admin toolbox) to prevent cross site reference forgeries from doing bad things. In this case if the feature were still there, a hacker could delete your images for you.

Note: if you enable gallery sessions, then the delete can be securee and the link will appear in the toolbox.