In my opinion, there may be a generational divide at play here. My students belonging to (Gen Z) seem to interpret portrait photos differently from me. For instance, consider this photo of the Spanish dictator, Francisco Franco. Although I do not find him sad or angry in this picture, my students do. I find it challenging to understand their perception.

While the dictator's expression is serious, it doesn't seem angry or sad to me. It's possible that younger generations, used to seeing people in countless selfie images, associate people in 'classical' photo portraits with sadness and anger because they are not depicted smiling or having fun. Unlike in selfies where they are often seen having a good time. This could explain their different interpretation of the photo compared to mine.

Sad or not sad Franco, that is a question.