The picture is lacking in definition; it's too fuzzy to get much idea of tire condition. However, the tire on the left side of the picture shows visible tread depth on the shoulder and centerline of the tire, and the tire on the right has good shoulder appearance.
Tires, even retreads, are very expensive. Relatively few landings come out of a set of tires. Dividing the cost among the tires by as few landings as are had, means every landing is expensive on a tire by tire basis. No one wants to let a tire get to a dangerous condition, but changing out a tire early is also not cost effective, and doesn't enhance safety either. Further, when the tire is removed from the wheel assembly, it's not like changing a car tire. The process is long and expensive, and requires nondestructive testing and certification on each component of the wheel assembly...all for a simple tire change.
For aircraft operating on a scheduled basis, such work is routine, and is done when the aircraft reaches a point in it's operation when the downtime can be had, and when it occurs at a base where the work can be done.
I don't see anything in the photograph, fuzzy though it may be, that might lead one to believe it's unsafe.