Inbox messages are of two types:
for each one the specifications are different.
|Suggested dimensions||192x192 px (must be squared)|
|Valid image formats||PNG, JPG (JPEG), GIF|
Width is constrained to 300 pt on app (px on web)
Height has the only limit of the screen height, so there is freedom to choose any height.
|Valid image formats||PNG, JPG (JPEG), GIF (animated too)|