How to make an image transparent?

[MinaGlaca]

This is my first time posting here, so I hope I did everything right

 

So I don't do image editing much (this is actually my first time using paint.net), and I need some help. 

So I created this image (It's for a forum signature, so it's supposed to be small): 

http://i.imgur.com/idMKuwH.jpg

However, when you drag that photo to your desktop and open it in a photo-viewing program, you can see the white spots in the four corners of the image. 

I want to get rid of that white space, like this: 

http://i.imgur.com/b0v6h9K.png

When you drag that image and open it, it does not have those white space I mentioned before. 

In paint.net, this is what it looks like:
Background:

http://i.imgur.com/RkSJnrZ.png

Layer 2:

http://i.imgur.com/8b2xgyj.png

Layer 3:

http://i.imgur.com/Fw9W9z6.png

As you can see, it appears that all 3 layers have those specific four corners transparent. 
However, when I try to save it it turns out like this:

http://i.imgur.com/KJQdlza.png

There is still the white spots in the four corners! 

How can I get rid of these four white corners? 

Sorry for the long post, and thank you!!!

[Pixey]

Hello Mina and Welcome to PDN .

 

This is how to get rid of the corners.

 

You must first draw a rounded rectangle on a new layer.

Select the inside of the rectangle,and invert the selection - Ctrl + I

Go to the backround layer and hit delete on your computer.

http://i.imgur.com/QG9s8Vq.png

End result:

http://i.imgur.com/nJif7mc.png

I hope this works for you.

[Cc4FuzzyHuggles]

To maintain transparency, you need to save images in either PNG or gif. PNG is often better. Please note though, that only PDN (paint.net) files can save in layers. So you will probably want your image saved in pdn as your project file, but then also flatten the image and save it as a png as the finished result.

 

Also, some programs do not recognize transparency, for example some photo viewers will make transparent areas white or gray when viewing the image.

Edited August 18, 2014 by Cc4FuzzyHuggles

[MinaGlaca]

Thank you so much for your answers!!!

It helped a lot