Print Composer Reference map

If you export the map canvas from Project > Save As Image you get a geo-referenced image output.

If you export from Composer using Composer > Save As Image you get a non geo-referenced image unless you check the option to Save World File under Export settings. However, I cannot get QGIS 2.18.12 (Windows 7 x64) to write a world file with Composer output. This has been reported before in QGIS 2.16 (https://issues.qgis.org/issues/15268) and was fixed but this may be a regression in 2.18. It might work in QGIS on Linux or OSX.

[aside: the empty reference map dropdown is still blank in my 2.18.12 even with more than one map in the composer.]

See the docs here and here for more info on how to set this up.

This was bug https://issues.qgis.org/issues/16924, which will be fixed in the next point release (2.18.13).