I am just a student and not a native speaker; but this intrigues me and I want to share my thoughts.
I think the object here is the record. So, "it" seems to refer to the pictures collectively.
Also, correct me if I am wrong, but the phrase "a record of dinner pictures" does not seem to necessarily imply various meals. It may also imply pictures of foods served at one dinner.
If the meaning of the noun phrase is taken to be the latter, I think the possessive pronoun "their" refers to the "plates of foods" served at the dinner; and the phrase "some evaluation of their satisfaction", therefore means the evaluation that Jack gave to those foods collectively.
P.S. Help me correct my use of the noun "foods" here. It is also a kind of "singular or plural" problems.
Student or Learner