I tried the AC app for the photo contest last evening because of this thread, which you have in different forums.
Anywhere I selected any photo from, the file appeared briefly, say 15 seconds, in the post field (with an x to delete), then a pop up said "could not upload photo to the forum" or something similar.
I know of one or two very experienced members who have never been able to upload to that forum.
Me - I always do it on my pc with the full website, no problems. I drag my photos there as backup.
I think the Tapatalk app or Tapatalk based AC Forums app should work, or the AC desktop or mobile website on the device browser but I haven't tried them. I recently switched from a 5.7" screen to a 4.5" screen temporarily and it's a PITA.
I would give up on the AC app, I use it for the blogs, but much as Android Central wants us to use it, it's quirky.
It may also be due to slow upload speeds with that app, mine are often not the best.