According to an article in "Nieznany Swiat" Magazine, the photo was taken at the end of June or beginning of July 1995 by Mrs. Maria Korejwo, a school teacher, in Katy Gorne [near Pustelnik Pinski] in Siedlce district in Mazowieckie wojewodztwo, Poland.

Mrs. Korejwo didn't see the object when the photo was taken. Note that the horizontal lines visible in the photo are clothes lines with colorful clips.

Kodak photo laboratory workers concluded that the film was not defective and suggested a possible explanation for the appearance of the acorn shaped object. They stated whatever the object is, the reason the photographer did not see the actual object, was simply because the object was moving too quickly!

Further analyses excluded the possibility that the photograph had been altered and stated that it was not a hoax.

Source: Nieznany Swiat [Unknown World] magazine, Poland By: Piotr Cielebias - "NOL - Eastern European UFO Journal", [http://nol-polishufojournal.blogspot.com/]