I picked up the dress on ebay - it was originally a floor-length, Grecian-style frock. It was square across the neck and back, the fabric falling from narrow panels which fastened with buttons at each shoulder. My re-working of the dress saw my shortening it into something more Summer-friendly. I removed the neck and back panels, and made shoulder straps from fabric taken from the hem.
For this collar I took the removed panels and remaining fabric, played with it it on the dummy for a bit, then hand-stitched the pieces together. Easy-peasy (just the way I like it!). It fastens with a couple of hooks and eyes.
I haven't yet photographed any of my project garments on live bodies. That is something I hope to do over the coming weeks, and will blog about shortly.