I'm trying to update my avatar, but keep getting an 'invalid image' message. I checked the FAQ but can't find anything relevant. Does anyone know the limits on avatar images here?

Open image in paint and save it as any format (and if necessary reduce size ).
If this doesn't work then try another browser or private browsing.

Thanks, the size limits were what I needed to know.

EDIT: Hm. I uploaded an image and it looked like it worked, but nothing has changed yet in the forum. Is there a delay of some kind?

It just has to be the same dimension for width x height and not necessarily the default 49 x 49px avatar size on GOG. The actual size of my current avatar image is 1014 x 1014px which automatically gets resized for the website but can still be viewed in full when the "forum_avatar" part is removed from the link.

I have one more question to tech assassin.
Please send some reply to ticket number T3HB2XX7.
Thank you.

That was probably it. The image in my account was updated, and the new image is showing on the forums now. Thanks for the help!