Resin oval cameos and settings. The settings have ornate scalloped edges.
The settings will fit standard
25x18mm cabochons, too (or use the cabs with metal oval settings, like the sample shown with a red metal rose).
Note: the backs of the settings are not completely solid.
I'd suggest G-S Hypo Cement, Glossy Accents or Diamond Glaze for adhering the cabs to the settings (and/or the settings to a collage). You could also glue on a bail plate to add a hanging loop.