(I'd seen that there was talk on the fltk forums recently about RGBA and images ending up with the wrong dimensions, but that's not my problem.) If you uncomment RGBA in test/dw_images_scaled.cc, does dragging the window around cause part of it to turn pinkish? (I'll attach a diff, even though it's not exactly difficult.) I had started by hacking up the dillo side to send RGBA, and it worked fairly well in general for images where every pixel is either completely opaque or completely transparent. Gradients didn't seem to work too well, and often these pink/red regions were showing up. So far it seems as if the value of green relative to the value of alpha is what can make it particularly lose its mind, but that's probably wrong. You know how first impressions are... I followed it down to fltk/src/x11/Image.cxx, by which point it had been transformed to ARGB which looked about right to me. Then there's lots of xrender and transforms and things I don't know anything about. I tried some setcolor and fillrect in FltkImgbuf::draw(), but it didn't seem to matter, so I guess that's not my problem... If the question is "Why bother?", dillo2/src/png.c currently just mixes in whatever the background color is the first time we see an image on the page.