Hello!

I am very new to the site and, also, very clueless on some things, as you can see.
I have noticed a great amount of users have picture messages as their signatures and I am really wanting to do it, too. I tried it once following this which only ended up with not only a white background, but absolutely huge in size.
Is the transparency and and the size only determined in the program you use to make your picture in? Or am I doing something wrong considering the the steps of the tutorial in my link?

I feel stupid asking this.
But thank you for your time.

EDIT: Also, the program I used for the picture my first time was MS Paint if that changes anything.