Not sure how big the image you're wanting to render is, but if is simply an icon you could first consider a simple formula field that renders an image in the details panel for the case that is in context i.e.
formula:IF(IsClosed,IMAGE("url for image if closed","case is closed"),IMAGE("url for case open","case is still open"))
If you do need to use a VF page, then you could leverage logic such as the following to conditionally render one of a number of images;
<apex:outputPanel layout="none">
<apex:image value="url to image for closed status" rendered="{!case.isClosed}"/>
<apex:image value="url to image for open status" rendered="{!NOT(case.isClosed)}"/>
</apex:outputPanel>