[WCF/Web Servics] WCF data communication parameters cannot be of Image type?

{"There was an error while trying to serialize parameter http://tempuri.org/:_image. The InnerException message was 'Type 'System.Drawing.Bitmap' with data contract name 'Bitmap:http://schemas.datacontract.org/2004/07/System.Drawing' is not expected. Consider using a DataContractResolver or add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.'.  Please see InnerException for more details."}