The original television systems were mechanical rather than electronic. They produced images by shining light through a rotating metal disc with holes in it onto a photocell -- this converted an image into pulses of electrical energy that varied by shading. The electrical pulses were sent via wire or radio waves to a bulb in a home set that shone through a similar disc spinning at the same speed. The more holes and the faster the rotation, the sharper the image. But it could only spin so fast and the resolution was pretty low. This wasn't the method that took hold.
TV as we know it was in part invented by a self-taught 15-year-old farm boy -- Philo Farnsworth -- who learned about electronics through technical journals that were left behind by a prior occupant of his family's home. He intuitively knew that the mechanical method wasn't the best way, and he started designing a method to generate and transmit rows of light and dark points to paint a picture onto a screen using electrons. He bounced his ideas off of his high school chemistry teacher, Justin Tolman.
His designs and obvious genius earned him the life savings of a couple of investors, and around the age of 20, he developed and patented a camera tube that took in images through a lens and focused them onto a photosensitive cesium oxide plate, which threw off electrons when struck by light. The electrons were captured and transmitted to a receiver. He dubbed it the Image Dissector.
But Farnsworth also caught the attention of the head of RCA (Radio Corporation of America), David Sarnoff, who had engineer Vladimir Zworykin working on electronic television, as well. Farnsworth, hoping for a licensing deal with RCA, let Zworykin have access to his lab for a few days where he was able to study the Image Dissector. He was impressed with the device, and some of its design ultimately got worked into RCA TVs.
Sarnoff offered to buy Farnsworth's company, but Farnsworth refused. Rather than pay royalties, RCA claimed that Zworykin had actually invented the first electronic television. Zworykin had filed for an earlier patent on his Iconoscope, which used a slightly different method for capturing images electronically, and had come up with a better receiver, but they couldn't prove that he had created a working model before Farnsworth. RCA kept Farnsworth in litigation for years and attempted to drive him out of business, but the fact that Farnsworth had built and demonstrated his electronic TV, and that his former teacher Tolman produced a sketch Farnsworth had made of his designs in high school, helped him win the patent battle in the mid-1930s. Toward the end of the 1930s, RCA agreed to pay royalties, but shortly thereafter, the U.S. government put a moratorium on television production due to WWII manufacturing material restrictions. By the time the war was over, his patents were nearly expired. He abandoned television, but his work contributed to such things as radar, baby incubators, telescopes and the electron microscope.