I was having the same issue back when I first joined too. There must be an image resolution maximum in addition to the file size limit, that's the only explanation I can come up with. My iPhone takes 4032x3024 photos natively, so it would be nice if the site would allow these photos since they are technically under 5.82 MB or whatever the heck the number is, but whatever. You can use a computer program to reduce the file size if your camera takes photos that are too large. I use a site called img2go.com, they even have a Chrome extension which is handy. I did some tests and have found so far that an image with dimensions of no more than 3000x3000px goes in perfectly fine. Hope this helps!