Custom Icons on Markers

Hi Everyone - I'm trying to use markers to highlight different types of communication within an office (phone, email, letter, etc.), and not all of the icons I need are available in the preset ones. Specifically, I'm trying to add an envelope icon to a marker.

I've tried adding the photo as a fill, and that just results in an envelope with a circle around it (though, I guess I could add a solid circle, behind...haven't tried that). I've also tried editing the photo file in ps, and then laying it over the marker, which works great at first, but once you hover/click, the icon is gone.

I did some searching on this forum, and saw something about editing the states, but wasn't able to figure that out. It looks like that post was from about a year ago, so thought I'd give it a shot, and see if anyone had a better way for creating custom icons on markers.

Thanks!