It's just a matter of cultural standard.
While including a photo may occur "mildly strange" to you (probably from a US background?) it is, for instance, in Germany as normal as stating your given name: You would just not hand in a CV without this information, even if (technically) it should not matter for the job.
The following is a quote from the "CV Recommendations for Students applying for Internships in Germany" from the Steuben-Schurz Gesellschaft. No emphasis added:
STRUCTURE: All German resumes include a picture either in the upper left- or right-hand corner.
...
Please include ALL of the following information.
1) Picture
All resumes must include a picture. This should be a face shot. Please make sure that this is a professional photo – a cropped picture of you at a party is not appropriate. Please scan the picture onto your resume before saving it as a PDF file.