Won't using ethereum cost a lot of fees to pay for upvotes? I think you will need your own blockchain for eliminating fees. How would you stop people from picking up images from Google and posting? Is it not possible to use distributed storage like Sia or Storj to store the media instead of a centralised server?
Yes we are considering running of our own blockchain.
You can't stop people from using any images they want.
This is called sharing.
Most of the images on Pinterest, Instagram or Facebook is already stored somewhere and each site offers sharing buttons.