Hi Carson
What kind of data type did you set this field to be? For example, the field name is "FilePath", you set it as "Text" data type and use "Media selector" form control. The data been stored would be the path to the image/file like "/mysite/media/folder/filename.jpg". Then in the transformation, you can use <%# Eval("FilePath") %> for ASCX transformation or {%FilePath%} for HTML.
Full example would be something like
<a href="{%FilePath%}">Link</a> or <a href='<%# Eval("FilePath") %>'>Link</a>