I would bet that you're uploading a high resolution photo that is very large in size, and it's taking up all of your RAM to upload it. You might try changing the resolution on your camera to something lower. You probably don't need high resolution, anyway, unless you intend to print them in a large format.
I also read that, if you are using an Android phone, a lot of people have solved this by going to Developer Options and uncheck "don't keep activities". I haven't tested this myself, though.
If neither of those help, please send me as many details as possible so that I can try to emulate the issue on my end. I would need to know the type of device you're using, the operating system version, the browser and version that you're using, and an email copy of the original photo.