1840s: Samuel Morse, American portrait painter, invents Morse Code, a code of dots and spaces that the United States government uses to keep messages secret from its political enemies.

Today: The United States constructs increasingly more sophisticated methods of keeping messages secret, and employs mathematicians to try to break the codes of other countries.

Early 1840s: Frenchman Louis Daguerre, a scenepainter, invents the daguerreotype, a method that uses a lens and light, along with a chemical reaction, to capture exact images. The first daguerreotypes are used mainly for landscapes— including the first photograph of Paris—and portraits.

Today: Photography comes in many types, including digital, and it is used in many educational, artistic, medical, and scientific applications. Photographs are also used as evidence in many police investigations and criminal trials.

Early 1840s: In the absence of any strictly enforced copyright laws, American...