How to change an image field content using workflow formula?

Hi There!

I have a custom image field. I would like to change the image of this field for a particular record using the new calculated field functionality.

I tried to create a public folder in the htdocs (imgs, let s say), upload the images with proper permissions and then return this URL in the formula. A mess! The field text indeed has changed, but the image remains the original one.

Any tips? Is it possible with current functionality?