Submitting a photo when you rate a meal is always nice. That way other people can better decide whether or not it's a meal they would like to try as well. However, if you're half-way through that delicious veggie burger before you remember that you didn't take a photo, don't worry about it! You can submit ratings without a photo.
What we find works best is to take a photo of your meal when it arrives at your table, using your phone's camera. Then, when you go to rate the meal in PlantEaters and click the "Add photo" button, just select the "From library" option and select that photo from your phone's camera roll.