The thermal image is overlayed over an outline image taken by the optical camera (about 1/2" apart), hence the ghosting at certain angles, the outline image is just there to help give definition to the image otherwise they all just look like blobs. The shot wasn't taken parallel to the tyre which I think is why the grooves look cooler on the inside edge, the tread is within 1*. The image on the opposite side shows the opposite so would tend to confirm that. In future I'll try to remember to keep the camera perpendicular.
I think the grooves might be hot because of the brakes transferring heat to the tyres, the rears don't show the same pattern at all.
Here's a (rear this time) tyre shot square on:
Yes, you could argue that the centre looks hotter than the edges, but again that represents only about a 1*C delta, and personally my tyres tend to die from feathered edges rather than worn centres.
If I'm going to put a bit of load in the back (or tow a trailer), I really don't want to have to drag out the foot pump as well, so I prefer to be prepared for a bit of load.