We are using fileupload component, defined by the resourceType "cq/gui/components/authoring/dialog/fileupload". We found this and started using while looking through the code for the WCM Core components.
It should be a mandatory field. In samplecontent-runmode "required=true" is working properly but in nosamplecontent-runmode even if Image is present, It throws validation failed message and prevent dialog to Submit.
