can you show pic's on two televisions from one computer using two apple tv's

You cannot send photos from the computer to the Apple TV. You can however start a stream from to Apple TV using the photos on your computer. Simply start to slide show on one Apple TV and then go and do the same thing on the other, you cannot sync the slideshows across 2 Apple TVs.

Yes if you are watching a slideshow on one Apple TV using photos from your computer, you can start a slideshow on another Apple TV also using photos from your computer.