Don't give up! If you find the right site to advertise on, (don't use keyword option use the option to find placements) you can find a winner.
I always start here to test drive a site before I use a media buy network like BSA. You can tweak banners, test traffic quality etc.
Once you've found a placement on google, go to semrush and compete to get traffic stats.
Usually image ads work best on a CPM basis.
Google normally take about 24 hours to review your image ad.
Like I said, the display network on google is good to test. Most of the sites on BSA and sitescout have Adsense.
Measure twice - cut once!