Dating Dewar's whisky bottle....
Your Dewar's bottle has a modern screw cap - which replaced spring caps during the late 1950s and early 1960s. That's a start. Next is the coat of arms - your bottle reads "By Appointment to Her Majesty the Queen" - this was used during two periods - the first from 1893 - 1901 and the second starting in 1956. Since a modern screw cap is being used, we know it's not from the earlier period. So, to try and be more specific, look at the reverse side of the label. A reference on the reverse side of the label such as ‘43-66’ means that the whisky was bottled in 1943. Take a look and let me know if you can see / read anything.