digital cameras made within the last 7 years or so add something called EXIF (exchangeable image file format) data to each shot. so you can view the exif data to see things like focal length, aperture, shutter speed, whether the flash fired, etc. and where lenses and cameras support it - things like distance to object, 35mm equiv. focal length, total focal length including teleconverters, photographer's name, time, GPS position, and other data.
you can view this data in most photo programs. but you can also view them in explorer, too. right click on properties then choose summary and advanced. on a mac simply hit command-i in finder.