my friend has a site hit 2-3% CTR and I ask for his ad placement. It seem the ad (blend with content) is close together with the images in post, and look like the images for the post, I think that's why it get a good CTR// take a look this, gv ur opinion on the ad placement whether it's safe or not for google..
as long as it doesn't confusing visitors it'd be ok, or you can add "advertisement" or "sponsor links" tag it'd be good but it could decreases your earning and ctr.