This is the Painting of the Madonna and Saint Giovannino
             by Domenico Ghirlandaio

The folkore sourounding this is the idea that the image in the background that is being pointed to is a UFO. Is it ?
The painting in the Palazzo Vecchio in Florence, attributed
to the 15th Century school of Filippo Lippi.  If you look in the
upper right section of the painting you can see a man and dog
that are apparently looking at something in the sky! See the  picture below for a blow-up of upper right section.

The painting you mention is indeed among the paintings
hanging in the Palazzo Vecchio, in Florence, Italy.  
Specifically, it is in the Loeser Collection and was
painted by  Domenico Ghirlandaio.  A small reproduction
of the painting appeas on page 17 of "The UFO Phenomenon"
volume of the Tim-Life Books, Inc. Series "Mysteries of the Unknown." They credit their reproducion of the painting
to "Scala, Florence." The museum is at piazza della Signoria, 
1  Phone number 055/2768325.

Couldn't find that particular one on-line, but a web search
revealed the following:
Jim

About the artist:
Domenico Ghirlandaio
 
 

http://www.comune.firenze.it/servizi_pubblici/arte/musei/eng/a.htm

 http://cgfa.kelloggcreek.com/ghirlandaio/ghirlandaio_bio.htm