Draupadi Ratha, Mamallapuram
Durga stands surrounded by attendants, in this photo from the interior of the shrine. Below her and to the photo left, a devotee prepares to cut off his own head as a sacrifice to the goddess. It is thought that this horrible rite actually did take place - not too often, one hopes - in Durga temples.
Durga's association with decapitation is attested by scenes like this, and also by ritual texts and myth (Mahishasuramardini). However, I do not see how an unaided person could possibly generate enough force and leverage to sever his own neck. It seems much more likely that he is cutting his own throat instead, in a kind of symbolic decapitation - which still, of course, results in his death.