What to do about jogs which won't open?

vlherring

I'm not sure where to ask this, but I have quite a few jpgs - each about 4mb in size give or take - which I saved to a hard drive but then when I tried to open in Preview [which. usually works] and then tried to import into Photos in neither case did it work. [using Mac OS15] the jpgs are from 2008 - 2021 - Is there any software which can open and make them useful? They are jpgs and yet Photos and Preview both say they are not in a recognizable file format.