I'm also experiencing issues uploading score photos. I'm using a 64-bit copy of Windows 7 on a PC. I've tried using Chrome, version 48.0.2564.103, and IE, version 11.0.9600.17959. The later of which I tried both in and out of compatibility mode. I also tried some different image sizes including: 379x379, 500x500, 1000x1000, and 612x816. I also tried the JPG, PNG and GIF image formats. None worked.
When you click the Upload images(s) button, browse to your file and select it, the image does appear in the Add "photo evidence" of your score section. However, when you click the Add Score button, the score is added to the list sans photo.