The pill with the imprint "K 8" is Oxycodone hydrochloride, 15 mg. Oxycodone is a pain reliever in the drug class known as narcotic analgesics. It's prescribed generally for the relief of moderate to severe pain. It is often combined with acetaminophen or ibuprofen.
The time-release version of Oxycodone is called OxyContin. Both Oxycodone and Oxycontin are considered to have a high potential for abuse.
Another pill that has "K8" on it, with no space between the two characters, is the sedative Clonazepam, in the dose of 1 mg. It's a white, round pill used to treat seizure disorders, anxiety disorders, and panic disorders.