600 DPI is the recommended minimum resolution at the final Size for a Rub-On Transfer Decal.  Working at higher resolutions are not a problem when using the correct Grayscale color mode. While lower resolutions may be just adequate for large shapes with no curves and only straight lines, almost all documents we receive have some small curved shapes and thin angled 1 pt lines or small light text. Whether these lines are part of some text, a border or another graphic, 600 DPI is the bare minimum if the rub on transfer is to resemble what you see on the screen. The line may appear solid on your screen, but if zoomed in you will find the line ditherers from 100% black pixels to gray pixels. Reproduced on your rub on decal sheet, the gray pixels will either be Black or will not be produced. If it is produced as black, it can make the line appear double the size compared to what you see on a screen view. If the gray is not produced, the line will be half the thickness. The results will be a line graphic or text that is either bolder than expected or thinner which may be broken during processing. An even higher resolution is needed to reprodyce line thickness of a 1/2 point. We recommend 1200 DPI. We plan to create & post the results of some tests at different resolutions to determine the minimum resolutions required to produce details of certain sizes.