2 questions: 1. I was just thinking, the image ads are CPM only, correct? 2. Also, I put in the code for the image ad only and I'm getting text ads, and it's taking up the whole space. Isn't that supposed to not happen?
I think only image ads are CPM. I do not think Image ads are exclusively CPM. Regarding #2, I think that if they can't find an appropriate image ad, they might give you a text ad before resorting to PSAs.
Image ads are not CPM. Image ads can be CPM or CPC. Adword campaigns that are keyword targeted can have both text and image ads and are CPC only. Adword campaigns that are site targeted can have both text and image ads and are CPM only.
It should be noted that someone has to target your site first anyway. Without that it doesn't matter what you pick, you will get 100% CPC
Follow up. CPM ads are images, or so I've heard, haven't personally confirmed, even if you select text in Adwords. Basically the text is rendered as an image.