I’m wondering if there is a term for the kind of photos where the subject and the background together form an optical illusion that they are connected.
The classic example is a photo of a person holding their hand out so that it looks like they are holding a large structure in the distant background in their palm.
Is there a term for this type of photograph?
The term you're looking for is 'forced perspective photography.' It's essentially a technique that exploits the limitations of human visual perception, thus creating an optical illusion where objects are made to appear to be a different size than they really are, or a different distance from the camera than they really are.
In addition to the more 'gimmicky' uses of forced perspective in photography, it is a technique that is frequently used in architectural photography in order to create scale, such as a real estate photographer making the rooms in a small house appear larger than it actually is, or a photographer making a space seem more 'epic' than it may actually be.
Though it's slightly off-topic for photography, I'll also mention that forced perspective is a frequently used technique in film and can be observed quite readily in most action movies as the technique is used to make the actors appear closer to danger (such as punches and explosions) than they really are. One of the more 'well known' uses of this technique in recent history is in Peter Jackson's 'Lord of the Rings' trilogy, where the director cleverly used forced perspective to make the actors playing hobbits appear smaller than the other actors.
Perspective Photography, or, Forced Perspective Photography.
Here is a flickr pool with many many examples.
This is a good starting point if you're interested in learning how to apply this technique with your own photography.
:-)
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