Preview won't work in DPX v8 (the OPs version), Gary without the http:// as v8 doesn't have the built-in server. (recall the same issues with Facebook badges as well?)
It will often just crash v8 (Not Responding) when previewing or just trying to add the placeholder bitmap. (It will be fine once published though

Click image for larger version. 

Name:	dpx.jpg 
Views:	128 
Size:	51.0 KB 
ID:	98352

But add the http:// and it will preview just fine in version 8.
Click image for larger version. 

Name:	2013-08-29_122515.jpg 
Views:	132 
Size:	76.3 KB 
ID:	98353