aren't pics also evidence of your mods?
Well in NY, it is mandated that you have a certified photo inspection done on a used or new vehicle, to show evidence of features, and exisiting damage if any. If on that photo, you indicate certain things that you have added, it can be used as additional evidence.
However, you just can't take a picture of you car at you house, and expect them to cover the items in the picture. Besides, that doesnt tell the insurance company what the item was worth, what make of the item and so forth so on. Reciepts are excellent, however, let it be known that if you have a custom paint job, you can expect it not covered unless you ask for it to be.