As far as I know, Garmin does not do anything like what Lowrance does with those raster images. You can save images to view from the sd card, but they will not overlay on the chart and you cant use them to navigate.

You could try trying using QuickDraw - but I havnt seen anything like that level of detail from QuickDraw on any of my scans or anyone else's. Things like brush, timber, rock piles etc just dont show up at all on QuickDraw. Even large features like ledges, holes etc are hard to capture.

You are stuck using waypoints as far as I know.

SonarTRX works fine with Garmin now but thats only for use on a PC.