I use Printed Treasures. They are already backed and pre-treated, so when it dries it is already permanent and there is no soaking. You can get a package of 5 (8 x 10) for $18.00. They are flexible and it will not wash out. No matter which ones you use, make sure you set your printer to good quality print, because fabric absorbs some of the ink and if the printer is set to medium quality or draft the colors will not be the same.
Maria