Correction regarding the names for those chords. My mind was wandering.

They're for using in the key of G, not D as I said. In fact the first (finger on second fret of C string) is the one to use for G ( it's not actually a chord but a dyad, since its only got two notes.)

The one with the finger on the D string is a C chord.

And the one with the finger on the G string is a sort of depleted D7.

But they work well enough for songs, whatever you call them.