I don't have an answer for the first question. PNGs are fine, however transparency doesn't work for avatars AFAIK.

And your avatar will change eventually... probably in a couple of hours o̶f̶ or days. ;) Apparently some people have the same problem: https://www.gog.com/forum/general/why_gog_updateschanges_user_avatar_slowly

Mine is 1200x1347 JPEG. It's glorious.

(note: it's very likely the forum resizes / compresses this)

My browser says it's 336x377. Also both and [url=https://images.gog.com/2a2fe569dc7fb9455bb5bc15a12569552cca82fe85fac0d7745d70b3f94f07eb.png]PNG, for some reason, where the JPEG has more saturated colours.

Right, same with me. But the original format can go higher than that. Some forums do limit this.

As has been mentioned, PNG images work - but transparency don't, neither in PNG nor GIF (nor does animation, for that matter). Why? The forum software will convert your image to JPEG, and create multiple versions of it - take Titanium for example:

"Full-size" (as far as I know, but Titanium claims differently in the post above) JPEG: 336x377
"Full-size" (Again...) PNG: 336x377 (do note the colour saturation difference between the PNG and JPG)
Image displayed as forum avatars: 49x49
Images in chat and forum quotes, among other things: 40x40 (displayed as 16x16 for quotes, and with a round border for chat and hover menu)
Image used in thread listing: 17x17

EDIT: There was also a 16x16 long ago, before GOG changed the system and replaced that size with a 17x17. If you change the avatar today, the 16x16 won't be made for you, a 17x17 will be used in the forum listing instead, the 16x16 is only created used if you changed avatar long ago. GOG made a change to serve images from images.gog.com rather than www.gog.com, and everyone who haven't changed their avatar before that change will have a 16x16.

Take me, for example, I have a , an "old" [url=https://www.gog.com/upload/avatars/2009/08/b40914c06351a6125b70a62aa9505b800a6727e2_t.jpg]49x49, as well as the original-sized JPEG (which was also 49x49, though the original uploaded image was a PNG), but since the change, GOG have added the new original-sized PNG, new original-sized JPEG, 49x49 "forum avatar" and [url=https://images.gog.com/867f7c9b030c5535825039970bd2b997e7a2696a56af8319d548366868fa95aa_forum_avatar.png]PNG, 40x40 "avatar medium"/avm and [url=https://images.gog.com/867f7c9b030c5535825039970bd2b997e7a2696a56af8319d548366868fa95aa_avm.png]PNG, and 17x17 "avatar small"/avs and [url=https://images.gog.com/867f7c9b030c5535825039970bd2b997e7a2696a56af8319d548366868fa95aa_avs.png]PNG.

If you check those, you'll notice that the images for the old system and new system have wildly different URL's, which is why I don't know of how to get Titanium's 16x16.

PHEW! Fuck doing that again.

Just checking something...

Weird... forum avatar can't be changed today?

EDIT: Hmm, fascinating, Maighstir. I actually found a backup of my forum images, and at some point in time, I made all sorts of formats for various forums, so I don't really know what I used last time I changed it here. Had to be ohhh... a good year ago?

Do you have any information about this problem?

You're not done, there are six of these suffixes:
_avs _avs2 _avm _avm2 _avl _avl2
:P

+1

(runs away)

Nope. Last time I changed my avatar was what.. over seven years ago?

EDIT: Grammar/spelling.

Ah, so.. the '2' ones are displayed on high-resolution devices? They're twice the height and width of the non-2 ones. And as far as I know the avl (avatar large?) one isn't used anywhere yet.

Anyway, as for sizes:
_avs: 17x17 (avatar small?)
_avs2: 34x34 (avatar small x2?)
_avm: 40x40 (avatar medium?)
_avm2: 80x80 (avatar medium x2?)
_avl: 64x64 (avatar large?)
_avl2: 128x128 (avatar medium x2?)
_forum_avatar: 49x49 (probably only until the forum is updated to the new layout, and thus use the new sizes)

And since _forum_avatar is only used in transition to new back-end system and front-end layout, there's no _forum_avatar2

In the old sizes there were also _t which was 16x16.

... in other words - good luck making one that's pixel-perfect in all sizes.

Thank you for your detailed answers :) The forum is being redesigned ? Do you know when it will be live ? I think that's good news

No idea when, but I thought it fairly obvious since everything except the forum and support pages have been replaced with a mobile-friendly layout, those two are the same now as when the site was launched in 2008, so logically they should be updated to match the rest of the site.

Hmm I need an image size that will show clearly in gog galaxy

Nm. Figured it out :)