I remember photos from the car's launch and in some, IIRC, Joest's helmet was on one front wing, Ickx's on the other, so that could be where the photo is from. The photos I remember were black and white, though, and I don't remember that photo (or even a detail from it) being among them, although it might have been.
I've tried a search in the forum, but even if it's in a forum thread it's likely to be gone, sadly, just like an awful lot of photos which have disappeared over the years.
I also tried dolomite's suggestion. I've never come across TinEye before, it looks like a useful resource but unfortunately the search came up blank.
https://tineye.com/s...1a449f85?page=1
Joest's 936 was labelled '908/80' at the time, I think because Porsche had given Joest the spare 936 chassis, 004, through the back door, so to speak, and they didn't have one for Kremer, their other main customer at the time, although Kremer subsequently built their own 936 with Porsche's help. I don't know if that was the real reason, and I've always wondered why Porsche couldn't just have lent Joest 936 002, which hadn't been used in 1979 and was still in the same spec as the chassis built up by Joest.