Should and investigator take photographs or video?
If the investigator is trying to document something that is not moving, photos are usually best. The reason is that resolution on a picture will be higher than that of video. Photos are great for inanimate objects such as cars, or houses.
If the investigator is trying to document something like a kiss or anything else that happens quickly (or is moving), video is better. Video is better because it is essentially 30 pictures taken every second. Therefore you don't miss the most important frame of action. Still images can also be taken from a video.
You can not get video from a photo. Therefore, video is better for situations where there is action.