Just apply the rub-ons to your photo as you would to cardstock, patterned paper, chipboard etc. You might just want to take the rubbing process a little more gently on your photo as you don't want the tool you are using to damage your photo.
Anyway here are some examples from some of my scrapping. Sorry the first layout was on black cardstock, so the black background I use pretty much blended into it, but you get the gist of it.
You can use the rub-ons as journalling. This rub-on is from AMM Expressions Rub-Ons "Love About You" and is available from my studio or online here.
Or you can use them as decorative elements either alone, or with the likes of Kindy Glitz, as above.
This ice-cream cone is from the Imaginisce Summer Lovin' set.
This is a pre-collaged patterned paper, complete with "Princess" title. All I did was add the photo, rub-ons and then the flowers with a brad and hey presto a great looking page. Simple but effective.
For a great of rub-ons to use on your photos and scrapbook pages, be sure to check what is in stock at the moment at http://www.scrapfx.co.nz/ and click on Shopping Cart.