A photo editor would be classified as an "app" (software or program), but file storage is on a computer's hard drive, a thumb drive, an external storage device, paid storage online etc. One has nothing to do with other in the sense you seem to be asking. In other words, photos are not stored in a photo editor.

Chromebooks have limited storage capacity; that's not their purpose. So they can't be a backup storage device.

A Chromebook runs on Google Chrome operating system. The editing software you can install on Mac or Windows is not compatible. You can try Snapseed, however. Most of its features now work on the newest Chromebooks. Additionally, there are online photo editors for Chromebooks:
https://www.howtogeek.com/360311/the-best-photo-editors-for-chromebooks/

.

I do everything in Photoshop. I have actions recorded that reduce any file I'm working on to 1200 pixels on the long side, frames the picture and adds my company name to it, and then saves it, setting image quality to 1 (low). Those images get posted to Facebook and Instagram. Speaking of Instagram, I'm a new Instagram user and hated it because it's a phone app. With the quality of today's smart phone cameras, I'm not posting pictures from my phone camera directly to anywhere on the Internet. Late yesterday, a friend showed me how to upload pictures from my computer desktop to Instagram. Definitely not something someone other than a computer geek would be able to do, but now I can post to Instagram with my company information and an appropriately Internet-quality picture.