This isn't as strange as it at first sounds. Sending pictures and sending sounds as electrical signals were separate problems. "Fax machines" that predated the phone were inventions to send images over wires. When telephone networks became ubiquitous, the technology was adapted a bit such that it sent signals over phone wires (mostly, adapting to the signal constraints imposed by the phone system.)

The earliest example of such a device is probably Alexander Bain's. It sent a drawing etched into a copper plate. A pendulum would "scan" horizontal lines of the image by swinging across the plate. The change in electrical potential between when it contacted the copper and when it did not was used to create electrical impulses. On the other end, a pendulum would induce a chemical reaction via changing electrical potential to re-create the image. Early devices like this were problematic in that both the pendulum timing and plate advancement were difficult to synchronize.

Frederick Bakewell improved in this with a device that used rotating cylinders instead of pendulums and images printed on conducting metal foil with insulating ink instead of copper plates. Giovanni Caselli's Pantelegraph was a bit more reliable because it used clocks at both ends to keep the devises synchronized. It used scanning pendulums like Bain's earlier device but images to be sent were insulating ink on foil like Bakewell's device. This saw some commercial success with a service to send images between Paris, Lyon and Marseille via telegraph lies (about 20 years before Bell's patent of the telephone.)

Early devices remained rather constrained in their input. It wasn't until the 1920's that "fax" machines were invented that could convert light intensity to an electrical signal, allowing one to send photographs or reproduce images printed on normal paper.