Is it legal to take pictures of the people who interview for a job at your company?
I think that you need a better system of interviewing and taking notes upon which to base your hiring decisions versus taking pictures of applicants. You should be using an application form that gathers legally allowed data on each candidate. You should have that with you when you conduct the interview so that you can refer to it. You should be using a structured interview (with standardized questions) that facilitates you asking the same pertinent job-related questions of each applicant. You should be taking copious notes to record their responses. Finally, you should have a worksheet that includes a checklist of the job qualifications (skills, character traits, abilities, knowledge, experience, etc.) for the job and a rating system (e.g., 0 to 5 in each area of qualification). You should then be able to come up with an instant total rating upon which you should be able to make a timely decision.
You should keep in mind that there are state laws that prohibit you from asking for a photo from applicants, so these would apply to taking photos of interviewees too.