Okay. This probably is not technically an ‘underbooby’ picture. With proper underbooby pictures you just get to see the underneath of the girls boobs; you don’t get to see the girls nipples.
I am old enough to remember when crop-tops that showed some underbooby were seriously ‘in’. Which would have probably been around the mid or late 70s. I can remember a girlfriend making an underbooby crop top to wear to a party. Which is basically just buying the right kind of tee-shirt, cutting it off at the right length, and then generally sowing a weighted seam around the front of it (so it did not ride up too easily and show too much underbooby). From memory she was even following instruction in a magazine (something like Cleo or Cosmo).
Ahhhh … those were the days. You almost never see bra-less crop-tops being worn out in the wild anymore. Only on the Web or in magazines.