How to handle images during software development

For software development one often needs images. But when I start working on an image I very fast end up with dozens of versions, like so

Start with a nice large scale image, let's say a photo from my camera(x.nef)
I do some adjustments on exposure correction and white balance, convert it to a x.jpg
start to add some little stuff by copying in various pieces from two other images. (a.jpg, b.jpg resulting in a layered image x.pdn
now I scale it to the required size and save it as x_small.jpg

By now I have 6 different image files floating around, and nobody but me knows the process behind them.

So the question is: How do you handle images in the development process?

Edit: Thx for all the great input. I combined various questions to my own personal best answer. But I accepted jiinx0r's answer because it really contained the missing idea for me to apply a naming convention for the kind of changes done.

Solution

file naming should be handled via a naming convention.

{name}-{mod type}-{size}-{version}-{create date}.png
{name}-final.png

e.g. 
file-white_balance-800x600-v01-20090831.png
file-white_balance-800x600-v02-20090831.png
file-final.jpg

the real point is to create an agreed on convention that people see the value in following (however simple/complex is necessary for your group). In my organization we do this for input/output datafiles, images, scripts, etc. (not the same convention necessarily for all, but that they follow something that was agree upon)

Hope that helps.