In photography, a merger is when an object in the background is right in front of or behind the subject. If the photo has more than one subject, a merger can also happen if the two main subjects overlap or touch the edges of the picture frame.
A merger can cause an object in the background to draw attention away from the main subject of the picture or ruin an otherwise perfect shot.
In photography, a bad angle can make it look like a tree is growing out of the head of a subject. Photographers should look at the whole frame and change angles as needed to avoid merging.