He has a loose thread on his shirt. His hair is a little unkempt (very unlike Brian), and he's a bad shave or something. This is not the dandy of Carnaby Street just a couple years earlier.
His haircut certainly was more ragged during '68 and '69 compared to earlier years. But it was also in with the times to be a bit more rock 'n' roll and unkempt whereas the '66-67 period felt more "dandy", as 24FPS mentioned.
I think it's pretty cool that he kept it at the same length while the other Stones grew their haircuts longer in '68-69, almost as if he didn't wanna mess with the Brian Jones trademark look.