Hi there,
You would have to do a little bit of keyword research to find which words or phrases yield the best results. Start with the Google Adwords keyword tool. You have to sign up for an account if you don't have one already.
-
Once you have established your account, make sure to uncheck the 'Broad' category and check on the 'Exact' category in the left sidebar area.
-
Type in varies keywords or phrases you already have in mind then hit search.
-
Review the 'local' results to find how many times a month that keyword is searched on Goolge. This should give you further insight on which words or phrases you should use on your pictures.
You can also 'View Source' on other competitors websites to see what keywords they are using to also get a good starting point.