If there is extremely high traffic on the Steam Network or if the network is temporarily off-line, you may not be able to upload or change your Steam Avatar immediately. Please wait a while before trying again.
If your file size is too large, you will receive the following error:
Missing image from upload. Try again!
You may upload any image as long as it is not offensive, vulgar, or specifically prohibited in the Steam Online Conduct rules. Your avatar may be removed and you may be banned from the Steam Community if your avatar is inappropriate.