How to make the background of the picture blank and just have the picture show

So I am trying to create my own health bar and its own system by having pictures of the health appear and disappear depending on the current health and I was wondering if anyone knows how to make the back boarder part of the picture that’s white disappear so that only the image shows and not its background.

You should be able to change the Alpha channel of the RGBA (the A part). 0 = completely transparent, 1 = completely visible

I did that but it just made the image invisible.