I have a button (an <img>) and i'm trying to find a way to making it floating on the page.

For example, you know that popups that appear inside the page and floats while we scroll the page up and down, but they stay in the same place without being scrolled?

I would like to have a picture doing that in the left and top side of my site, that img has and hyperlink.

lets assume that the img code is this one:

PHP Code:
<a href="www.radio.page.pt"><img src="http://www.downloadsgospel.com.br/arquivos/radio.gif"></a