I am not familiar with Vuforia (although it looks interesting, I'm going to try it this weekend!), I may have a suggestion.
Is it possible that Vuforia does not know what to do, since WebCamTexture images WebCamTexture instead of something like Texture2d ?
WebCamTexture is Texture ( Texture2d , WebCamTexture , RenderTexture all extend from Texture , but they cannot be exchanged).
So, try converting your texture and transferring it to Vuforia?
var tx2d = new Texture2D(); tx2d.SetPixels((go.renderer.material.mainTexture as WebCamTexture).GetPixels());
EDIT: What I found here in the Running in the editor section:
There is a specific Web Cam Behaviour script.
To use the playback mode for Vuforia in Unity Pro, simply select the supplied or built-in webcam that you want to use in the Camera Device menu, and then activate Play Mode using the Play button at the top of the UI Editor.
You can also use the standard Unity Play mode with the non-Pro Unity version and the setting "Do not use the Component of behavior for the playback mode in the webcam.
To use standard playback mode, adjust the conversion of the ARCamera object to view the entire scene, and then launch the application in Unity Editor. There is no real-time camera image or tracking in the standard Play Mode, instead, all targets are considered visible. This allows you to test the non-AR components of your application, such as scripts and animations, without having to deploy them to the device each time.
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