Now I'm no expert here, but I have read that if humans are shown faces and something else, they always look at faces. So I can speak for myself that when I see such a slide I find it very difficult not to ponder upon every detail of the mugshot (such sad eyes...hmm...are those eyebrows....now that's some scar, wonder if he got it while biking etc....). By the time I'm done studying this remarkable face (blown up on a gigantic screen, mind you), not only have I missed the hugely important data that this mugshot apparently generated, but my focus on the seminar has also substantially diminished.
For PI's who have a burning desire to show a mugshot in middle of their talk, my suggestion is to NOT show the data on the same slide. Show the picture for a few seconds, then move on to a slide that has the data but no picture....PLEASE!