Can't insert HTML code into textarea

Hello,
I’m trying to use a text area, and into it I want to paste an html code.

Basically, I want to make it easy for users to copy and paste the code on their website. (it’s a picture with a link to my site)

The problem is that the HTML code is actually “used” by wordpress and doesn’t stay into the textarea.

That’s the code I’m using…
<textarea>image and link code</textarea>

thanks!