Tacking irons and spatulas are commonly found in the entourage of tools for encaustic; mainly described as an alternative to the heat gun when fusing a painting. However, they have many other uses such as adhering paper scraps (small and large) and like items (photos) to the surface of a encaustic piece. They can also be used to manipulate (sculpting and painting) the wax surface; this is particularly with the heated spatula (not pictured), due to their various interchangeable points.
Paper collaging can be tricky; particulary with scraps that are smaller than the tool. A practical way to collage paper is to lay down a background of color, or better yet, a layer of medium. Pigmented wax (encaustic) can actually hide your imagery, and by using medium first, and encaustic after, you can avoid many of the troublesome issues of the color hiding imagery- such as a photo. It is good to know that most paper, especially white and natural fiber, will turn transparent when it soaks up a lot of medium.
