I am having the same issue, but I noticed that Google hangout will push through the pic not allowing other to see it. With the stock messages app, I was get an error that said the file type was not supported. I opened the picture from my gallery and went to edit. Once it popped up, I hit save. I was then able to send the pic fine.
It has happened to me sometimes. I'm consulting with a samsung professional he said my phone has uploading or downloading problem but i don't see any problem
Has there been any resolution to this? I've recently had this problem, only with one friends' messages. She also has a GS5, and its only pictures taken by her phone, she can send my downloaded images. Also I noticed that I can save the attachment, and the picture appears as a thumbnail in the Gallery but not as a full picture.
This is the only post I could find through Google.