just a little list of where you can upload your images to
1: Gravatar, go to the photos part (ive never used the Mobile UI so it's probably not there) and maybe refresh and then upload the image, it's convient as it's near where your profile image is
2: steam, use the artwork section to upload an image. Mobile players probably don't have it though. Screenshots can also be shared
3: IMG something, can't remember what it was but I've heard it isn't available in some countries, but I'm sure I saw a gif on it and many people her use it
4: Google photos, it doesn't work and you have to view the image to see what it is, I wouldn't recommend it
5: Simpleplanes.com, if you do the custom thumbnail trick with a image then upload it as unlisted, maybe multiple images at once if you want to, then you could technically upload images to SP.com, image transparency not guaranteed.
6: discord, the images will expire and turn into a missing image, please do not use it

There's more stuff too, X/Twitter, facebook, blah blah blah. You could use anything that supports image uploading, Heck! Even stuff like a game's Wikipedia website could be used to share images.
I know I've used Roblox once to upload an image.