I read somewhere that uploading images using the built-in browser (as opposed to Chrome or Firefox or what-have-you) is generally the solution. Since I switched to using my native browser (Galaxy S4 Mini) for uploading photos instead of Firefox (which is what I prefer by miles and miles), I have no problems uploading, though the actual image doesn't show until after I post. If I've accidently uploaded an image twice, or missed one that I was planning on, I just go back and edit. It can be a bit of a pain, though, because I can only upload one at a time.