Whilst Photographs are sometimes a good way of comparing height, the further they deviate from the perfect pose, the harder they become to use as reliable evidence. A perfect photo for comparison requires several main requirements:
1. Both subjects are an equal distance from the camera.
2. The shoe sizes are equal, or at least known.
3. They have similar posture, which in some photos is hard to tell.
4. There is no horizontal tilt in the picture and the camera is at least at their face level.
5. The floor is flat and level.
Yes, common sense stuff really, but 90% of photos won't be near perfect. As soon as you start to get away from this ideal set of conditions for 'perfect photos', judging the actual difference is open to interpretation and prone to a larger margin of error. Click this thumbnail below and consider that both pens are identical height. Depending on the distances from the camera, the angle of shooting, height differences can be emphasised or reduced.
The problem of perspective can never be underestimated. It can play havoc with the truth. I lose track of the amount of visitors who submit photos on this site as evidence, when the perspective is skewed in favour of one of the actors in a picture, the footwear can't be seen, the postures are different etc. I've lapsed myself in that area. Also, when mugshots are used as evidence, they normally always don't reveal the actual height of the celebrity standing beside the height chart. You have to consider how far the person is standing away from the board and how high off the ground the camera is. Think about this image below (click it)
Ideally, in the first image this would be perfect for showing as close to the true height as possible - the camera lense being the same height as the person. As soon as you deviate from this, then Line Of Sight becomes an issue. If the camera is sitting shorter than the height of the person then from the lense it will appear as if the person is taller than they are in reality (the second image). If, on the other hand, the camera lense is above the top of the person's head (third image) then they can look in the photo shorter than they actually are.
Just bear in mind the idea that photos, whilst handy, are only a part of guessing height. In person comparisons, especially when you can compare a celebrity standing beside someone of known height - like a friend - are in my opinion a better method than relying solely on photos or video footage alone.