No ornamentation should be played strictly in time- then it sounds like it's a series of notes versus an embellishment. Play both with and without mordents, it'll sound more of an embellishment if you can think of it that way.
Um. Well, I beg to differ -- at least in the Bach and Frescobaldi and Pachelbel I used to play on the organ, I felt it was best to have them strictly in time. But -- I also expect that it is at least partly a matter of taste, and certainly a matter of style; in romantic music -- say Chopin -- I play ornaments very freely...
The top picture, first execution is incorrect.Mordents start on the auxiliary note: D-C-D-C
I would have to disagree. Bach was very capable of writing out the notes if he wanted to; ornaments shouldn't have to be taken literally at all times. It was also common baroque practice to insert ornaments and embellishments where the performer sees fit.