HR (in the USA) is very sensitive to anything that could lead to a claim of discrimination in hiring. So, consider two candidates that have nearly identical resumes. Candidate #1 has a portrait showing him to be a white male that is physically fit, and in his 20's. Candidate #2, with essentially the same background and experience has a portrait showing him/her to be NOT a white male in his 20's (choose your own picture for Candidate #2, they could female or non-white or age 50 or overweight or disabled or whatever). The company has only one job opening and offers it to Candidate #1, NOT because of their portrait, but because of some minor difference in their resume (maybe they listed one class that the hiring manager recognized as being somewhat useful and that class was not listed on Candidate #2's resume).
Candidate #2 then files a lawsuit with the state employment agency claiming discrimination in hiring.
So, what does HR do? They immediately eliminate both Candidate #1 & Candidate #2 and hire Candidate #3, who is less qualified, but does not have a portrait on their resume. If there is a REASON for the portrait to be included (eg you are trying to get a job a TV sportscaster), then fine - in that case the job posting will probably specifically request a portfolio of pictures.
Oh I understand now. Thanks for the explanation.