TransparentCameraBar is a jailbreak tweak that allows you to make the UI featured in the stock Camera app transparent. The jailbreak tweak, free on Cydia's BigBoss repo, is a way to trick yourself into having "more" real estate for the view finder.
I should mention that this is more like a WinterBoard theme, than a tweak that impacts the photo's end result. If you take a photo either with, or without this tweak, the end result will be the same. It's simply a visual tweak that zooms in the camera UI to give the appearance of a bigger viewfinder.
Take a look inside for more info...