When I try to upload an image using SteamNetwork, the chat shows that the upload is complete, but if it is an 'XXL Picture Frame', the following error is displayed on the console and the image is not uploaded. You have to compress the image to lower the size considerably to be able to stick it up...

What image are you trying to upload? 

The file is a PNG and I am trying to download and paste it from a DropBox URL.

Image files of the same size can be staked in the RakNet environment, but this does not work properly in the SteamNetwork environment, and in some cases even 100 KB image files cannot be staked.
This situation only occurs with 'XXL Picture Frame' and not with other picture frames.

I have the same issue! i managed to upload some images on some XXL Picture Frames that where 2048x1024 on size and worked fine! later tried different pictures of the same size but could not upload! resized the images on photoshop to 512x256 and still getting the image is more than 1mb on chat! 

All i get is the 'image has been added to queue' - but nothing happens.
This is since switching over to steam network and query port.

The steam network and query port changes shouldn't cause any issues unless you don't have a dns or your firewall blocks webrequests which would mean your server wouldn't even connect to steam. If you guys actually link me the images you are trying to use or won't work then I can test the issue.

Same problem here
it have something to do with steam networkink
when i switch back to raknet than its working fine

ok,so here are some images im trying to load! these are the lowest quality so far ive made!
https://i.imgur.com/z5zb1t0.jpg

https://i.imgur.com/PfUdlFF.jpg

https://i.imgur.com/jg6OmPu.jpg

https://i.imgur.com/cvqcnH3.jpg

I have more images i can share if needed!

ok ill test this out and get back to you thanks for the links

no problem!

I am not running raknet and made the queryport changes.   everything is working fine.

if you are running Linux make sure you have the gdiplus installed.

Got the same problem. Can't upload most regular pictures that normally all uploaded previously. When i make the same image smaller, almost unreadable, it will post. But as long as it is it's normal size it says: image was succesfully loaded to the sign but it stays empty.