The copyright issues are only really interesting if you want to contribute to OpenStreetMap (OSM) (which may also have been your question in its initial version. Please be sure to not upload anything to the OSM servers if it is not really useful and copyright-problem-free data. Most questions and answers here on this site are about contributing to OSM. If you collected tracks with your GPS by walking, cycling, driving on roads/ways (not by mousepainting on a google satellite image or google maps), then it might be useful for OSM. But, that is not your question *now*. However, you could help OSM with your GPS tracks if you want to.
Yes, you can make Garmin maps (.img) from OSM data (.osm). That process is called [rendering](//wiki.openstreetmap.org/wiki/Rendering). Not easy! See section "Creating your own maps from OSM data" on [OSM_Map_On_Garmin](//wiki.openstreetmap.org/wiki/OSM_Map_On_Garmin) if you are interested.
And before that … you need to get *from gps tracks* (we often call them gps traces) *to osm data*: you could use an OSM editor (do not upload!) like JOSM for the conversations (gpx track → data layer way and add a `highway=whatever` tag to all). Merging all gpx files into one before might save mouse clicks in JOSM. However, that will not really be a map then, but likely usable on your etrex.
All in all, as Simon already said, you are not really at the right place, I think. But it may work, if you put much effort in it. … And while doing that you get to know the OSM tools which you may need for contributing later on. ;-) This would be the better way: become an OSM contributor and help to improve the public OSM data with your collected gps traces and knowledge. This will take a while and needs some learning and a slow start. Then you can use any OSM-based Garmin map (after they have updated their databases) and have very good maps.
