http://iqdb.yi.org/ searches a few sites. 4scrape, konachan, danbooru mainly. all have plenty of wallpapers but there are a few NSFW here and there. uses downloaded images or links to images. useful for finding similar images.
you can use that or 4scrape, danbooru or sankaku channel.
you can use that or 4scrape, danbooru or sankaku channel.