When split testing images on Facebook, do you duplicate the same ads in a campaign so each image you test gets the appropriate amount of click/impressions?
Also do you focus on newsfeed ads or the smaller ads?
facebook doesn't always distribute traffic evenly over all the ads in a campaign so it can be hard to give each one a fair shake.
I usually create a lot of duplicates with lower budgets so the chances of each ad getting a fair shake is higher.
Even so, I can sometimes have 10 campaigns duplicates with one image in them, same demo, budget, ads. and the cpc / ctr % throughout those 10 camps will all vary +/- 75% , so who knows :P
best thing to do is just experiment and test. when you find a winner scale it slowly but surely and don't make big budget changes too often. I'd recommend 20-30% increase 2-3 times daily if you are scaling a budget, and even that can sometimes set it off into the loony bin.
gl
Always split test your images in seperate campaigns, don't do what most do and use the 6 image ability. Your traffic won't be split evenly, competition amonst ads etc.