I'm not familiar with Vuforia (although it looks interesting, I'm going to try that out myself this weekend!), I might have a suggestion.
Is it possible Vuforia doesn't know what to do because of the images being
WebCamTexture instead of something like
WebCamTexture is a
RenderTexture all extend from
Texture but they aren't exchangeable).
So, try to convert your texture and pass that on to Vuforia?
var tx2d = new Texture2D();
tx2d.SetPixels((go.renderer.material.mainTexture as WebCamTexture).GetPixels());
EDIT: What I found here, under the section
Running in the editor:
There is a specific
Web Cam Behaviour script.
To use Play Mode for Vuforia in Unity Pro, simply select the attached,
or built-in, webcam that you want to use from the Camera Device menu,
and then activate Play Mode using the Play button at the top of the
You can also use the standard Unity Play Mode with non-Pro Unity
versions and by setting ‘Don’t use for Play Mode’ in the Web Cam
To use standard Play Mode, adjust the transform of the ARCamera object
to get your entire scene in view, and then run the application in the
Unity editor. There is no live camera image or tracking in standard
Play Mode, instead all Targets are assumed to be visible. This allows
you to test the non-AR components of your application, such as scripts
and animations, without having to deploy to the device each time.