I'm looking for image reapers, it allows you to download all images from a website for reference.
I was told about this by someone in the game industry.
The type of software you're referring to is known as crawlers. Google for 'image crawler' or 'site crawler' and you'll come up with several.
Haven't used one of those in years so I wouldn't know what to recommend specifically.
But this saves only what is currently on screen, a crawler follows every link on a site and for example downloads every image it can find that matches some spec set by the user.
Like send one to 4chan.org and it'll go into every thread on every board and follow every image link and store what it finds.
No, that doesn't save what's only on the screen... When you save a whole webpage with your browser, it replicates the html code and downloads all images referenced by the webpage, so you can view the page offline.
But if you want more features, then you want what was suggested, a crawler, that you can set to "crawl" down as many series of links on a page as you want to find more images.