>ah i see. what ever the change was, even if you only have hits of it. let me know
It's just "THUMB_SETTING" in config.php. I think one of the issues was that changing the format broke all the existing thumbnails that were in the previous format

Optimally, kokonotsuba should just support generating JPEG thumbnails with the appropriate background colors (for OPs and replies respectively) when a PNG is uploaded - this is what other imageboard software does, including 4chan

I tried adding this functionality myself a couple of years ago, but I'm not a programmer, so I only got as far as getting a single color to work