i discovered some points which you have to take it in your consideration if you are working to deisgn a WCF solution,specially the security issues with WCF :
1) You can't apply Message Level security with WCF Streaming which is used to pass Large binary data between the service and WCF Clients.
2) In Case you want to apply WCF Streaming on your WCf Host,you have to change your security level from message to transport level.
3) Maximum received message size to a WCF service is 64 KB;if the message exceeds this limit size the WCF runtime will throw an exception.
Note : if you want to increase the Max. Message Size,on the Bindings properties you can change/increase the message size as per your request.
Hope this Tips helps WCF Architect and Developrs :)