I've got two generic MJPG cameras from different manufacturers.
Both can and do serve a raw image in a web page.
Trying to add them to a control page, I get these errors:
WebServer http://192.168.0.34/live returned type multipart/x-mixed-replace; boundary=myboundary (image required)
WebServer http://192.168.0.35/mjpg/video.mjpg returned type multipart/x-mixed-replace; boundary=--myboundary (image required)
Neither camera has authentication turned on. I supplied the control page with same url that works in a browser window.
I have a Foscam C1 that properly displays in the same control page.
Searched the forums, but I couldn't find general requirements for this, just lots of help for specific cameras. I'm particularly puzzled by the second one, as that's a very high end AMX camera that is rock solid.