How do you use .img files? I don't have a Garmin device. Possible to convert them to use in Android?

Someone shared a map of an entire country with me via Google Drive. He rides a motorbike with a Garmin 64s and has extensively mapped a lot of the roads in this country on his Garmin device over the span of a decade. Unfortunately he's a bit clueless on computer matters so he isn't able to explain to me how the files work.

I don't and have never owned a Garmin device. All I've got is Basecamp on Windows.

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I've got these files on my hard drive:

Laos_Map.img - 22MB

gmapsupp.img - 22MB (oddly, *exactly* the same filesize as the above)

Southeast_Asia.img - 490MB

These don't open in Basecamp and apps like MAPC2MAPC can't open them.

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I'd like to take these maps and, at least,

1) get them to open on a desktop app like Basecamp, and ideally

2) convert and load them into an Android mapping app like OsmAnd (conversion into an .sqlitedb file or some other non-proprietary standard)

I'm completely unfamiliar with Garmin .img files, what the various files are, and how to use them. Are the maps this person has spent a decade making basically locked to Garmin devices?