How to attach image from a list of predefined images?
These are general guidelines as I made something like this but for D6.
I would create a logotype variable in template_preprocess_node and then loop on you dropdown variable. For each value selected I would add an &lt;img src='path/to/logo1.png' alt='Logo 1' /&gt; to your logotypes variables.
Then just display the variable in you node template.