Two sites on Ruche-inghttp://www.quiltersfancy.com/ruching.htmhttp://www.thimbleworks.com/ruchemar.htm
this is what my sewing book has to say about ruching:
"Ruching is always cut on the bias to give the fabric more elasticity. This technique is used extensively in couture dressmaking. Small areas, such as waistlines or bustlines, can be ruched, or a whole bodice can be treated in this way. Be prepared to spend some time arranging the gathers, and take care to avoid pulling them too tightly.
1) lay the garment our or on a dress form and deciede on the area to be ruched. Makr one row of basting along the top and bottom of this area. measure the length and depth of this area.
2) Cut a strip of fabric on the bias twice as deep as the makred area by its length. (this also depends on the fabric weight, for example, chiffon is cut 3 times as deep as the marked area)
3) Baste along both edges of the fabric strip under by 1 1/4". Stitch two rows of gathering stitches across one short end, and gather it up to fit across the marked garment area.
4) Pin the gathered end of the ruching to the garment at one side of the opening. Kepping the garment pulled tight on the dress form, stretch the ruching around the body of the garment. Pint the ruching to the basted lines (done back in step 1.)
5) After stretching the ruched fabric around the dress form, handstitch two rows of gathering stitches across the ends to fit the ruching. Pull up the threads, and pin. Trim any excess ruching next to the gathering.
6) Position the gathers in the ruching. Working around the garment one section at a time pin the gathered ruching in place at the side back side, side front and center front. Position the pins between the folds in the fabric.
7) Take the garment off the dress form, and stitch the ruching looselybetween each pinned gather. The stitches must be very small, each catching only one thread of the ruching. Remove the thread tracing. The ruching at the opening is covered by a facing or a zipper opening.
I hope that can be of help.
the sites mentioned are showing the tool used to do ruching to make fabric flowers for projects... the stuff I got from my sewing books is about garment ruching....
the technique shown in the pic you have... I'm not sure what thats really called....