Understand perspective, distortion, and warping.
In photography, perspective refers to the relationship between a camera's location in space and the scene being photographed. Depending on the vantage point (the camera angle and camera distance from those elements), objects may appear smaller or larger in a photo than they do to the naked eye. Lines that should be straight may bend a little near the edges of the photo. This is called perspective distortion, and you can fix it with a little photo manipulation using Perspective Warp.
What you can do with Perspective Warp.
Make your photos look more like what you see with your eyes, and add objects that blend seamlessly with the elements of the original photo.