This photo was taken in the spacious and most interesting botanical garden of Friedrich Schiller-University in Jena, a city in the German state Thuringia. By the way, for most of the 20th century, Jena was a world centre of the optical industry and I think that each of us knows the name Carl Zeiss.
In one of the tropical houses there I saw this little guy, a poison dart frog, about 4 cm long. They are native to tropical Central and South America.
The photo was taken through a thick pane of glass.