No, not a DNN skin, I was referring to a 'Repository' skin. The repository module can be skinned separately from the overall site skin.
Since you didn't understand what I was asking, I'm going to assume ( I know ) that you're usign the default repository skin, in which case it's doing exactly what it's designed to do. In the default skin, you can upload a file and an image. The image is displayed as a thumbnail image that will display in a new window as the full size image if clicked on.
If you want to change this behavior, you need to select a different skin ( on the module settings page under the Repository Settings section ) or modify the default skin so that the thumbnail image is not 'clickable'.
To do that, copy the /DesktopModules/Repository/templates/default folder and paste it in the same location, renaming it to 'mydefault'. In the new /DesktopModules/Repository/templates/mydefault folder, edit the template.html file with notepad and make the following change..
find this line..
<A HREF="[IMAGE]" TARGET="_blank"><IMG SRC="[THUMBNAIL]" BORDER=0 ALT="Click to view"></a>
change it to...
<IMG SRC="[THUMBNAIL]" BORDER=0 ALT="">
save the template.html file with your changes.
Now, go into the Settings for your Repository Module, and in the Repository Settings section, select 'mydefault' as the repository skin.