Height Differences in photos can sometimes appear bigger or smaller due to numerous factors.
For instance in this photograph below, taken on a flat solid tiled floor, this represents a real 4-inch height difference.
5ft 8 Rob vs 6ft Jenny (wearing heels)
In the example above, a couple of factors are at play which might make you think the difference is a bit more than 4 inches.
Firstly, the camera is a bit below my eyes, so even though I'm standing side by side with Jenny, the top of my hair will appear a fraction lower in the photograph than it would have done, were the camera placed at the same height as my hair.
The second factor is that Jenny possesses a smaller head than myself - nearly 3cm - so if you are comparing height based on eyelevels or chin level, this might fool you into thinking the difference is more than 4 inches. My eyes are at the end of her chin, which would normally be indicative of a 5 inch difference. Hair can also add a contributing factor, although in this case Jenny's hairstyle isn't particularly thicker than mine.
Here are the actual measurements before this photo was taken of Jenny in heels and myself barefoot.
Rob barefoot is 5ft 8.25
Jenny in Heels is 6ft 0.25