You can click on the  'Insert Link ' Icon or type the text into your post directly, either way the link you want to post needs to be placed in text between [url] [/url] tags like so.

[url]http://www.mywebpage.com/myimage/myimage01.jpg[/url]

Alternatively if you want to hide the full link and display a short messahe instead use the following format.

[url=http://www.mywebpage.com/myimage/myimage01.jpg] Whatever Text you Like [/url]

This will display the link as "Whatever Text you Like", rather than the full http://www.mywebpage.com/myimage/myimage01.jpg