Imagen in forms

Hi,

I have a form (tipo_panel) with product, cost and product imagen url. The images are on another web (www.something.com/imagen/producto1.gif)

I have another form (reserva) with a dropdown to select the product. When you select the product, I want to show the apropiated image but i can't. I have a field to show the textual image url, and it works perfectly. I have create a formula field with this formula:
"<img src='" + input.Imagen1 + "' width='64' height='75'/>"
but i doesn`t work

¿How can i show images of the select product?

thanks