If this addiction to the pictures is really something you feel you need to break, you have to cut off all easy access to them. Delete all the ones you've saved and block any websites you go to. Of course you can unblock those easily in a moment of weakness, so put in a completely random password that you cannot possibly remember.
If still can't stop cheating and you really feel that this fetish is detrimental to your health, get rid of the internet completely at home. Unless you work from home, you do not need the internet, no matter how much it can feel that way sometimes.
If these aren't really options for you, you could try to build either negative associations to the pictures (to deter you from even wanting to look at them) or positive food associations (to help you eat better when you do look at them) by spending time looking at corresponding pictures each time you look at the obese animals. It may seem silly, but the brain is incredible when it comes to forging these associations.
