The Glowforge can engrave any normal JPG or PNG image from the internet, but it will not cut them. In order to cut you need to have a Vector File. Vector files differ in many ways from normal image files, primarily they can be endlessly scaled without any pixelation. Vector formats are PDF, SVG, AI, EPS, & DXF. You should use SVG files for cutting and scoring on the Glowforge
If you want to make a normal image into a vector file, then I recommend using a free and open source program Inkscape. Within Inkscape you can import an image you would like to print and give it a border so it will be cut out from the rest of the material. Or you can trace an image to create a silhouette that can be cut out. Once Inkscape is downloaded and Installed, I recommend also importing this template specially made for Glowforge. It will give you all the proper guidelines and limits for a sheet of proof grade draft board, streamlining the design process.