It seems that the avatar photo has to be reduced down to 6 KIB. How do you do this?

I used an image manipulation program (Gimp) to scale (or re-size) the image down to 90x90 pixels (the default maximum avatar size). Then you can save it with variable compression down to 6KB or less.

At some point, I changed the maximum size for avatar pictures (the picture associated with your name that shows up on every one of your posts) to 8192 bytes and 150 x 150 pixels. You can use a photo editor like Gimp to crop, scale, and compress your avatar jpeg photo to fall within the limits. If you would prefer, send me your photo and I'll do it for you at no charge (limited time offer, side effects may include discomfort, shortness of breath, shock, heart arrhythmia, and paralysis -- and that's just what happens to me!).