It's really easy to make your own bottle cap necklaces.
You can either flatten the bottle caps yourself or buy flattened ones at your craft shop (often to be found in the scrap booking section).
The self adhesive resin stickers only cost a few bucks for a few dozen.
Instead of using double sided sticky tape to attach your picture to your cap in the last step you can also use strong glue.
That said, I find that too messy and therefore prefer the tape. :)
First you decide which word you'd like on your bottle cap necklace.
Next you place the self adhesive resin sticker over the word and make sure it sticks properly.
Then you cut the superfluous paper off, until you only have the round resin with the word underneath.
Next you place the resin + word onto a double sided sticky tape and cut the superfluous sticky tape off.
Pull off the sticky tape's protective layer and stick the whole thing to your bottle cap.
There you go - done! :)