Creep shot
From wipipedia.org
A creep shot is a photo, taken surreptitiously and without their permission, of a person or part of a person whom the photographer finds attractive. For example, it might be of the breasts of someone in a tight top, the bottom of someone in a tight miniskirt or of a woman in a bikini.
Such photography is unlikely to be illegal, but this should be checked locally. However, it may be annoying to the other person and if done persistently might be regarded as a breach of the peace or harassment.
