One cannot tell by looking, and 'guessing' is nugatory. Measure your chain and if it's more than 0.75% and less than 1% elongated, change it; and if the new chain slips on any of the sprockets (more likely the middle ones) then change the freewheel. If the chain's more than 1% elongated (already), do what Dan (above) says. Happy riding for many miles thereafter.