DDS TGA and graphics issues

[enric]

I'm very bad at graphics .
I try to add an image on the info of a unit, the image should be transparent with the background.
I tried using an already used image by BA: shoot marks, and it works ok:

shot.jpg (39.94 KiB) Viewed 1690 times

But if I modify the image and put my image, the resulting file is not more tranparent:

Screen Shot 2013-07-27 at 10.07.37.jpg (52.45 KiB) Viewed 1690 times

Probably is a stupid thing but I don't know how to make it transparent.
Any help please.

[enric]

Solved with Graphic converter.