Absolutely!
There is an app at the App Store called Touch Icon Creator. It's $0.99 (USD) and I use it often.
It allows you to pick your own picture to make an icon. So, what I do is usually find the logo for the site I want to make a homescreen bookmark. I save the picture to my Photos. Then, open the app and it'll let you add that picture to the URL.
Makes the icons look very professional. If you save a lot of bookmarks to your homescreen(s), this is very nice.
Hope this helps.
Marilyn