Ever wonder why most DSLR cameras capture images with a 3:2 aspect ratio, while most other cameras use 4:3? It’s because they were designed to match different things:
Common aspect ratios in still photography include 4:3 (1.33) used by most digital point-and-shoot cameras, Four Thirds system cameras and medium format 645 cameras; 3:2 (1.5) used by 35 mm film, APS-C (“classic” mode) and most DSLRs;
[...] The reason for DSLR image sensors being the flatter 3:2 versus the taller point-and-shoot 4:3 is that DSLRs were designed to match the legacy 35 mm SLR film, whereas the majority of digital cameras were designed to match the predominant computer displays of the time, with VGA, SVGA, XGA and UXGA all being 4:3. [#]
Prints have been around longer than digital cameras, so that’s why your compact camera photos are cropped when you try to have them printed as standard 4×6 prints (4×6 prints have an aspect ratio of 3:2).
Aspect ratio [Wikipedia]