1) These are clear glass cabochons, with a designed mix photo image on paper adhered to the back. The image is well adhered and not prone to deterioration under normal use
2) there are a total of 12 designs, usually they come in pairs. include 9 or 10 designs, sometimes 12 designs depending on the size you choose  
3) a good craft glue or adhesives should be used to set these into or onto the findings. There work best in a finding that is enclosed at the back to eliminate the showing of the white paper. Please see photos for practical application  

4) package per size  
10mm 12mm 14mm 16mm 18mm is 50pcs per bag
20mm 25mm is 20pcs per bag