Digital cameras take photos of a different length to height ratio compared to that of traditional film cameras. Traditional film cameras take photos that fit a 3:2 print ratio. Typically 6x4inch or 10x15cm. Digital cameras on the other hand, often take photos that fit a 4:3 ratio originally conceptualised from your computer monitor (640x480, 800x600). A 4:3 ratio does not fit most standard traditional film print sizes.
Refer to the below guide for print sizes, for photobooks photo collage posters and calendars