To study ufo images, you need many similar ufo photos to back up your idea.
You also need to confirm what species are inside the disk shapes ufo. in other word, you need to identify those species first.
Do any experts have such information? I do not think so. Then how can they make a conclusion? They only study ufo logically, they usually avoid mentioning those images from the sky.
This is not an alien mechanic craft. These kind of shaped UFO are formed by a few energy type of space lifes. ( new edit : it is alien's biological energy craft )
reference article: http://ufo-spacelife.blogspot.com/2007/09/shape-of-ufo.html