Keeping some temp files while deleting most

Is there a way to keep certain temp files easily while deleting all the other debris from the internet?
When we visit our own website we get temp files I want to keep so our site loads quickly. Our site has lots of pics and having it load faster is nice for when I work on updating the pics of items we have for sale. I would like to "keep" our files/pics so they load faster. At the same time I want to delete the other debris that builds up. Most rexcess is to sites or pics I will never go back to (not intentionally anyway).
I have an ftp folder with all of our sites files/pics in it. Is it possible to allow the computer to access those files as it would temp files without changing them? Or to create a temp file for the machine to use without having debris go into it also?
I'm not sure if I'm posting this to the correct place or not but if you can help me or tell me where I might ask it will be appreciated.
Steve Robinson
[email protected]