When: Spring of 1963, based on the slide mount and elements of the photo.
Where: Atlantic City, NJ. While it was expected that this scene would have changed quite a bit in 50 years, it was not too overwhelming to get a general location of the scene, thanks to the spotting of the (unfortunately) since demolished Warner Theater. Thankfully though, the boardwalk in "AC" still brings crowds, though the scene differs quite a bit with the passage of time.
Who: Lots of folks, but all are anonymous.
How (much): Purchased from one of my favorite ebay slide sellers for $5.99.