Hi webone,
You can use for that the typography plugin "HTML" by clicking on button "2".
When you select option "HTML" for the link field, click on button "+". In the textarea try to fill the following code:
<a href="/$cck->getValue('name_of_field_link')" class=""><img src="/$cck->getValue('name_of_an_image_field')" title="" alt=""></a>
Do not forget to move an image field to a "hidden" position.
Regards,
Mehdi