A Google image search of "tessellations" will result in more options than you will need. Try the following link to get started.
"Tessellation" refers to a picture in which all of the plane is filled with no gaps or overlapping areas between items included in the picture. The base of the term, "tessella," is Latin and means "small square" - a tessella was an individual small piece of clay, glass, or stone used as part of a mosaic.
Today, possibly the artist most known for his work with tessellation is Maurits Cornelis Escher, usually known as M. C. Escher. This Dutch artist lived 1898-1972 and is recognized for his intricate artworks featuring tessellation, architecture, and illustrations of buildings and objects that could not be physically built.
Check out the link below for many examples of Escher's work. You should be able to find something there for your class.