I haven't made any bottle cap bows yet. In fact I haven't made any bows yet, I'm just getting started.
I do however, make bottle cap earrings and pendants.
Here's what I do. I have a image program called GIMP that I downloaded free off the internet. I take and open my image in that program. There is a little figure that looks like a scalpel that is called a crop tool. I use that to crop my images. If I have a page of images I can use that to chose just one image or I take and cut the images that I don't want out then cut and paste the images I do want into one area of the paper.
If I am using a single image I then size it to 25mm.
Once I have the image printed on regular white card stock I cut it out then use modpodge to glue it into my bottle cap. I use Easy Cast resin on my bottle caps. This is stinky and better done in a garage or outside. Some people might not want to mess with this so there is and alternative available. Epoxy resin stickers are available at http://www.etsy.com/
You can get bottle caps and images on there. If you are looking for images search for bottle cap collage images