Tread depth is calculated as the measurement from the upper edge of tread to the base of the tire.
Winters typically come 11/32 to 13/32 new (higher performance tires come with less tread, for less squirm under load), and you typically don't want to use a winter tire with less than 6/32nds of tread remaining. So while those 8/32nd tires look pretty damn new, especially compared to summer/all-seasons, they don't really offer more than one season of good performance.
Or, to calculate their value, Pirelli snows are typically 11/32nds. Those tires have only 40% of their life left, so they should be worth 40% of the original purchase price. Also keep in mind tires lose their capabilities as they age, so 40% is being generous.