I used the windows Snipping tool to cut out the icons I wanted to use, then went into GIMP and cut out the border. I also gave mine a bluish border. Then I scaled them to the size that I wanted.
This process probably took me about an hour to do 4 icons but that was because I had never used GIMP. Doing one now would take me about 15 minutes.

Here is an example one I use for Healing on the bar.
Heal1Icon.png