As an average traveler I’d like to be able to say that the main was ok, or was too salty, the roll was stale, or frozen (the latter could be airline’s fault but they should know what to improve), and that the dessert was canned sugary faux fruit, etcetera...
A required photo may be asking too much, as some people do not know how to do that, but you still want their input.
Without breaking it down to separate fields for comments on each dish, I think you should be able to post all your comments (e.g., too salty, frozen, dry, etc.) in a general comment field. That being said, I think people really need to be encouraged to take a picture and upload it, since most of the story can probably be conveyed with a single picture, and I think the ultimate value of a site like this may be just to showcase the contrasting appearance of meals between different airlines, caterers, etc.; how some airlines may be procuring much worse meals than other airlines, though from the exact same caterer; and how some airlines may be serving a meal that it 10x better for passengers traveling from Europe than the one served for passengers traveling from the US. So I really think you need to get people to post at least one photo, in order to help make an impact.