I found this information in the Frequently Asked Questions at the bottom of the page (faq):
Problems with images
Please make sure the image you are attempting to upload is a format FatSecret accepts (.gif, .jpg). Next, make sure the file name is simple and short, with no spaces or funny characters. If this doesn't help, it's possible that the image is corrupted.
Someone who is busier than you is working out right now.
There will come a day when you can no longer do this. Today is not that day.