One of the ways to fight against this is to allow only text posts. Any sub that allows pics and gains enough people, the photos tend to float to the top. A clever pic is low engagement and can be consumed and upvoted in seconds. Add to this that the photos probably show on sites outside of reddit (like imgur) and often times you can upvote/downvote on these other sites!

Text posts with lots of good discussion take a while to consume. People passing by won't even bother to click on it and you will not be able to see the content outside of the sub's page itself.

IMO upvote/downvote buttons should only be in the entry itself and never on a front page. You have to at least click on the thing to up vote it or not.