If trying to load photos from an iPhone the newer software has a built in sizer. Not sure when this was added or if it was always there and I just missed it. Screen shots below showing how. Since I figured this out I have not gotten the size error selecting medium quality. Once you have selected a pic to upload at the bottom of you phone click choose image size and select medium. Once loaded click load full image and no one will have to open your pic to see it full screen.