Anyone Know What's Caused This?

Thanks again to all the replies.

Friend has got a new SD card, tried a different lens (you never know!) and updated the firmware. Still happening.
He sent me a raw file which shows it below. All I can see are green dots. Image is untouched in LR but obviously has been converted to an lrpreview jpeg for viewing. it looks different to the original images suggesting the in-camera jpeg processing is doing something funny with it.

I think it's "back to Canon" time.

8iNNtgI.jpg


Then a 100% crop
jBWKYQW.jpg
 
Yep, back to base repair looks to be best bet. I wouldn't be surprised if the sensor turns out to be Donald Ducked..
 
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