A radio "Image" file is the file you get when download from any radio.
You should always download this Image file from every new radio before you play with it. An older radio, say you just bought you should always first read the Owner's manual and do a complete "Factory Reset" before downloading and saving this file. This will remove the previous owner's settings. Label it so and then go ahead write out your new file from it. Go ahead and "send to radio" again saving the new file renaming it as a new filename your choice.
You will have now your original Factory Image file for backup and of course, your new frequencies file which you can pull up at will: edit/add/remove frequencies, etc.. Never lose that original Factory Image file.
Radios have many Settings, most are fine left alone Factory default. The more complex radios such as DMR/DStar/C4FM/P25/NXDN have many more settings that have to be altered to work specific repeaters, Groups even to make the radio work at all. If you are not sure what a specific setting is, look it up first in the Owner's manual and/or the Internet before you change it. A great way to learn the more Advanced Technical sides of all radios.
Kenneth Strom VA3KRS