Anyone know how to apply transparency/alpha to any image?

[E.D.Revolution]

I've been playing around with Paint.net and GIMP but I can't seem to apply any transparency to the image itself. I don't mean alpha by painting or making the background transparent. I mean the whole image. Does anyone know how to make an image, itself, transparent? I don't want to resort to a GIF editor program to do it for me. I'm trying to get the image to a specific transparency for my own purposes.

[Sligneris]

Post deleted

[Kroki]

If you want to make an image with a low opacity it's impossible on .gif format, you have to save your picture as .png.

[E.D.Revolution]

Layer -> Transparency -> Add alpha channel.

Then use selecting tools to remove usually white background.

I don't mean alpha by painting or making the background transparent.

Sorry, but that's not what I'm asking.

Perhaps I'm not asking it correctly. How do I apply transparency to something like this in Paint.net or GIMP to make it translucent?

[Kroki]

...?
This picture is not translucent in any way.

[E.D.Revolution]

I know. It's fully opaque. I want to know how to make something like this translucent on GIMP or Paint.net.

[Kroki]

On Gimp, on the layer window :

This jauge represents the opacity of the selected layer, 0 is transparent, 100 is fully opaque.

[E.D.Revolution]

Ah, I see. Thank you!

[Phantom]

Just so we're talking with Gfx program-related terms for other people that might have trouble in the future:

You're trying to set the opacity of a LAYER (the image you're currently working on) to absolutely nothing, or 0.