Sisko's imagination of Buck Bokai
Imagination is the ability to form images in the mind. Elim Garak once commented "The truth is usually just an excuse for a lack of imagination". (DS9: "Improbable Cause")
In 2369, several aliens studying the crew of Deep Space 9 took the form of people from their imaginations, including Jadzia Dax, Buck Bokai and Rumpelstiltskin. The aliens had never experienced anything like it and found it to be extremely unique. (DS9: "If Wishes Were Horses")
Garak would often say Julian Bashir had an active imagination when he questioned Garak about his past. (DS9: "Cardassians", "Second Skin")
When Damar expressed his interest in picturing the conflict between the Prophets and the Pah-wraith, Weyoun warned him that too much of an imagination was dangerous. (DS9: "Image in the Sand")
During a vision being sent Benjamin Sisko by the Pah-wraith, Wykoff told Benny Russell the Deep Space 9 crew were all in his imagination. (DS9: "Shadows and Symbols")