I'm being a bit picky here, but IOS is an operating system that runs on Cisco networking equipment. "Images" is how one refers to the software that is loaded on the switch/router/etc. For example, I can buy an "layer 3 enhanced image" for a Cisco switches that will give me limited routing capabilities.

For that reason, one should be careful about the case of the letters when referring to IOS and iOS, as they can lead to confusion if not used appropriately.