Explained in post 15, purple Chica's gun on the tripod, you can't tell if it's full auto or semi-auto from the picture. You can't see enough detail.
The M1919 is harder to tell, you have to open the cover to see that the right sideplate is thicker and the cam is different to preclude machine gun parts from being installed. It is, in fact, legal to own every part of any Browning M1917, M1919, M1921, M2 or the AN/M3 series EXCEPT the right sideplate of the receiver. However, someone with a drill press and a good set of files could make one from SAE4130 flat stock. During World War 2, receivers for those guns were turned out by machine shops as far removed from the gun industry as AC Sparkplug, Frigidaire, Kelsey-Hayes Wheel, National Postage Meter and others. The old line gun companies mostly produced barrels which took specialized machinery. Any high school shop class could build a complete M1919 machine gun receiver from stock steel given a set of blueprints and a clueless teacher.
From a practical standpoint, the only reason semi-automatic versions of belt-fed machineguns even exist is the possibility of owning a real machinegun legally was made un-affordable by the Hughes Amendment in 1986. One market for them is re-enactors and living history buffs. Unlike a drug cartel gunman, they are not seriously hampered by a "non-machine" machine gun. Decals and a paint job do not turn your 1.2 liter four-banger into a race car.
The semi-autos are fabricated from real machine guns which various governments around the globe have deemed obsolete and sold off as surplus. There are companies who import these guns, and in bonded warehouses, destroy the parts the ATF requires destroyed. In the case of a Browning pattern machinegun, the part is the right sideplate, and since 2005, the barrel. The semi-autos are built from these parts sets which have had the right sideplates removed and destroyed. A new thicker sideplate with a different set of camming surfaces is riveted in and the internals replaced. The thicker sideplate means that the it is not possible to install the full auto parts as they are bigger than the available space.
As one of the more successful designs of the 20th century it was produced all over the world by at least 80 countries. During World War 1 water-cooled guns of this type would fire barrages of 100,000 rounds a gun a night. That's 400 belts of ammunition, they would add water now and then, replace the barrel every 50 belts or so and keep on hammering. I own one. It will still do that and the thing was built in 1918.
http://www.wikileaks.ch/cable/2009/03/09MONTERREY100.htmlThe State Department cables released recently by WikiLeaks confirm that our government is very aware of the fact that U.S military munitions are finding their way into Mexico, and into the hands of narco-trafficking organizations, via a multi-billion dollar stream of foreign military sales and Pentagon arms exports. Many thousands of the M1919 series guns were among the military weapons the Pentagon sold to El Salvador, Guatemala, Mexico and other Latin and Central American governments.
So based on the metal link belt hanging out of the left side of the gun it looks like it is in .30-06. .30-06 besides being the service cartridge of the US for over seven decades it was also used by every Latin American country except Argentina and Venezuela, Greece, Norway, Denmark, among others as a military cartridge, particularly from after WW2 until recently.
So, odds are your sweetheart's gun came, as Euro mutt pointed out, "... at a rock-bottom price from some Central American military armorer who'd had it sitting in a corner of the armory since the end of the Cold War."