Years ago I tried being a photographer and worked for someone who did weddings. His equipment included these large flashes, pretty old school. One amazing effect was the light could see right through a lot of women's summer dresses. That's what is going on here.
I used to have a lot of fun editing the images because during the wedding's reception, I'd take hundreds of images with that flash, obviously focused on the hotter women in the crowd. And when I'd get to editing, it was like I was able to undress those girls. I'd see their panties or if they weren't wearing any. If they were shear panties and they had bush, i'd see that, too. I'd see tits all of the time. It was a wanker's dream. I'm sure I still have them and should look one of these days; they'd be on CD-ROMs in my storage. I don't even have a CD player anymore.