It could have been both, it was pixelated as hell.
It's henna
It looked nothing like a bra strap guys, her clothing wasn't overlapping it, it literally stopped half way and there was just skin.clothing overlapping bras/bikini is pretty common, the terrible quality of the photo also made it kind of hard to distinguish. I initially thought it was a tattoo but it did also look like a zebra-ish patterned bikini strap (where the pattern is cut off at a point)
Y'all were just in denial (And one of you still is by the looks of it! )