It can be worth it.
I run a celeb photo/wallpaper site and use google.
I get approx 1200 uniques and 60k pageviews a day and make anywhere between 1-5$ day in adsence which is not to great.
I found CPM is better for photo sites, however they are had to get into with good pay rates. I make 0.10 per 1000 page views any the company cant fill all my inventory so its only displaying about 25k banners during that.
I currently run Adsence and a CPM campaign on my site and the CPM banners make more. I wont run popup ads, as I hate them. But i think intersitals(sp?) would work well, forcing a ad display between some pages.
Google is for text based pages. Photo pages dont get good CTR. You get alot of PSA's and need to add Key relevant text to photo pages to trigger adds. This is not easy trust me.
Google can work, but you need good traffic numbers for it to pay off.
I will also say that the better your site is, the worse your ctr is. When I first started my site was not a the best, and I was getting $100+ month from the same traffic. Now with the site looking good and working right I am lucky to break $50 per month.