Well, first you need to make sure the data from that topo map is not copyrighted and that you get permission to use that data under a CC-by-SA license from the person/company who made that map.
Please note, this is very important: We at OpenStreetMap never ever want copyrighted data to be imported in our database unless there is a specific grant from the copyright holder!
So if the Garmin images are provided by someone who says ‘please do what you want with it, I don’t care’, but you can intelligently suspect the data to be copyrighted by someone else, then you cannot upload the data into OpenStreetMap. And I really suspect this to be the case here, so I’m not going to tell you if it’s possible and, if so, how you can import this.
