Copyright and licenses:

images/exit.png: Taken from the software Zikula. Developed by Zikula
Development Team and licenced under GNU General Public License v.2 or
any later license.

images/grass.png: Copyright 2009 Thiago Leucz Astrizi . Released under
Free Art License 1.3 (http://artlibre.org/licence/lal/en).

images/hourglass.png:  Copyright 2009 Thiago Leucz Astrizi . Released under
Free Art License 1.3 (http://artlibre.org/licence/lal/en).

images/house.png: Copyright 2009 Thiago Leucz Astrizi. Released under
Free Art License 1.3 (http://artlibre.org/licence/lal/en).

images/normal.png: It's a derived work os an image usen in the game
FloboPuyo, developed by IOS Software and released under GNU General
Public Licence v.2 or any later license.

images/number.png: Copyright 2009 Thiago Leucz Astrizi.  Released under
Free Art License 1.3 (http://artlibre.org/licence/lal/en).

images/tree.png: Copyright 2009 Thiago Leucz Astrizi.  Released under
Free Art License 1.3 (http://artlibre.org/licence/lal/en).

images/wall.png: Copyright 2009 Thiago Leucz Astrizi.  Released under
Free Art License 1.3 (http://artlibre.org/licence/lal/en). 