When part of a subject in a photograph appears to be larger than the rest of the rest of it or larger than than the other objects in a photo, this is called Perspective Distortion. Perspective distortion, which is related to focal length, appears to increase as the camera gets closer to the subject.
A good example of Perspective Distortion would be the result of a very close up portrait of a face. The nose will appear to be much too large compared to the rest of the person’s face.
The best way to eliminate Perspective Distortion in your photographs, is to take them from a sufficient distance from the subject. This can allow for bringing the entire subject into the image as well. Also, using the proper lens is wise. A short to moderate telephoto lens is recommended, which would be a lens in the 50mm to 125mm range.
There may be times when you want there to be some distortion of perspective in an image, for artistic effect. It can be used to emphasize certain aspects of your subject or scene for example.