It would be funny if it weren't so sad. Also, you will be tickled to know that many of these people were of German heritage.

From a newchurch wedding.

At the last Novus Ordo parish I attended, whenever there was some sort of blessing being given to someone, the priest would ask us all to extend our hands to impart the our blessing upon the individuals as well.  The people looked just like they do in the picture above.

For example, a new person being accepted into the RCIA, or a new Eucharistic Minister or member of the "Greeting Ministry, The Religious Education teachers at the beginning of the school year, etc.  

We probably had a half dozen of these little ceremonies a year.  I never put my hand up because I didn't think that my "blessing" had any value.  Of course, the congregation was never asked to actually do something worthwhile like "pray" for the person or persons being "blessed".

Where does the novus ordo practice of imitating the "nαzι salute" come from?

Are novus ordite leaders trying to set the Church up for embarrassment?  They did that in the past with insisting on ɧoɱosɛҳųαƖ men becoming priests and then looking the other way.  They could be doing this again so in the future if the Jєωs need to milk any bribes out of novus ordo organizations, they could use this kind of stuff to embarrass the Church publicly.

What is the origin of this one handed salute?

This is an old Roman salute. Nothing more.  

Sorry, but this is irrelevant to the photo.  In the Novus Ordo, the priest doesn't invite the crowd to "salute" the person; he invites the crowd to extend their hand to bless the person.  The fact that it looks reminiscent of the nαzιs is just an interesting tidbit and the reason it looks rediculous.  The so-called blessing is the poor theology and the problem.  It is certainly "more" than a "old Roman salute".