How would you react?

I've been dating a guy for about 4 months now, but I've noticed he still has photos of him with an ex-girlfriend (almost fiancè) on his facebook page. I feel like if he was really over her, he would've removed them. But I'm not sure what to think or how to feel. He's told me about their relationship and why it ended, so I can't understand why he would still have those pics and why he would still be friends with her on facebook. Am I over-thinking this and making a bigger deal about it than I should? Should I say something to him about it? I feel like it's eating away at me a little, but I can't figure out exactly why!