Optimizing for Google image search is not difficult, it just requires good on-page optimization and including the target keywords in the image file-names and alt tags. The hard part is getting the images indexed; while the Google spider indexes pages as quickly as within hours or days, the spider only indexes images every few months. To get your images indexed all you need to do is have some quality backlinks pointing toward the site and wait a few months.
Once your images are indexed you will likely immediately see high rankings for your target keywords in Google Image Search. If you rank on the fifth page for a keyword in the normal SERPs you should rank on the first page in image search, mainly because there is less competition in image search.
The easiest way to succeed with image search is to have lots of images, the more images you have indexed and ranking the more traffic they will bring. Most of the images on Naruto Wallpaper bring 100s of uniques per day while some bring 1000+. Knowing which keywords people search for in image search is not as easy as it is for the normal SERPs so a lot of trial and error, or brute force is required. The more images you have, the more likely you will find the good keywords which bring 1000+ uniques per day.
Each new backlink helps the entire website’s rankings, so if you have a sales page or something similar on the website each backlink will boost your SERPs and in turn, sales.