The best thing to do is...

1) Google Images, find whatever image you want i.e. twitter

2) Open image, zoom in so the image fits your screen nicely

3) Bookmark it (screen shot will be of the image)

4) Obviouslly call it Twitter, and change the url address to twitter.com/home

Bit long, but works great. All my bookmarks look like apps!

Hope that helps.

Follow me on twitter @SurajMeghani