Legal Question in Real Estate Law in California

It is "legal" to take pictures of your neighbor's property, or anyone else's, for that matter. It may be a civil wrong (a tort, such as invasion of privacy) to do certain things with the photos, such as posting pictures of nude sunbathing neighbors on the Internet. Even this would probably not be "illegal" in that it's probably not punishable as a crime. (The usual meaning of "illegal" is something that is forbidden by law, and most lawyers do not consider the term "illegal" to include things which might result is a civil action for damages without criminal liability).

The photo-taking process you describe MIGHT also involve a minor trespass to land, if, for example, the tips of the ladder rails poked over the property boundary, or the camera lens or the photographer's hands crossed the property line. Trespass to land is a civil wrong (tort) but the acts we're discussing almost certainly are not criminal trespass as defined in the Penal Code, sections 602, 602.8, etc.