This is a picture of a Sebastopol Clasp medal which was awarded to the combatants (and medical officers) who were present at the siege of Sebastopol during the Crimean war. The siege lasted a year from September 1854 to 1855. You can see these medals on display in the regimental museum based in Hamilton, Central Scotland.
This part of the collection of British Army medals which have been awarded to members of Scottish regiments. You can find other pictures of medals in the medals photographic section of this site.