Apparently I don’t have permission to upload my artwork. Why?
Have you tried linking to a url?
Maybe your post count isn’t high enough, might be worthwhile to contribute something constructive or fun in the community boards https://forums.unrealengine.com/forumdisplay.php?10-Community
When I was in your situation I would just upload the image to imgur or any other free image hosting site and then use the “From URL” option when inserting an image.