Hi everyone!

I’m running Piwigo with the Bootstrap Darkroom theme and this plugin: GThumb+ (mosaic thumbnails). I’m trying to add a tiny 21×21 “AI” badge (diamond SVG) on the bottom-left of each thumbnail for photos that were AI-processed (Upscaled / Enhanced / Colorized / Denoised). Ideally:

-Badge overlays the thumb (positioned absolute), with a simple tooltip and i18n text.
-Works with GThumb+ mosaic layout and lazyload.
-Minimal/no theme edits (prefer hooks/prefilters or a small plugin).
-(Nice-to-have) Show a short “AI note” in the picture information panel too.

I experimented with template prefilters and hooks like loc_end_index_thumbnails (to attach per-thumb variables) and loc_begin_picture (for the single photo page), but ran into compatibility quirks with GThumb+ and some “by reference vs return” differences across versions.

Questions:

-Is there an existing plugin or example that overlays small badges on GThumb+ thumbnails?
-What’s the recommended hook/template target for safely injecting per-thumbnail HTML with GThumb+ (without hard editing theme files)?

Pointers to docs, sample code, or a known pattern are super appreciated. Thanks a lot!