A variety of high-resolution blank check templates can be downloaded from the web (e.g., offers free downloads of a high-resolution JPEG image). Any graphic software (such as Adobe Illustrator or Corel Draw) can be used to place a mock address on the blank to give it the appearance of a real check. Two different black pens can be used to create the initial text ("original" ink) and a later addition ("suspect" ink), as shown in Figure . The following two generic gel pens were used in this work, a Papermate gel pen (used as the original pen) and a Sharpie felt tip pen (the suspect pen). A mock forged receipt can be prepared by typing a text with an inkjet printer, followed by addition of new text and/or symbols later using a different printer (Figure ). LDI MS analysis of mock forged documents. An Autoflex-III (Bruker Daltonics, Inc., Billerica, MA) MALDI/time-of-flight (TOF) MS was used for all small-scale measurements. The samples of both pen and inkjet printer inks on paper were collected by cutting out small (ca. 2x2 mm) pieces of either document and attaching them to the sample stage using a double-sided Scotch tape. No chemical treatment of the samples was needed, and no MALDI matrices were applied to the samples. Imaging measurements were carried out using Autoflex Speed MALDI TOF/TOF (Bruker Daltonics, Inc., Billerica, MA) mass spectrometer, where a large piece of document was attached to a 3" × 5" stainless steel target. External calibration was used in all measurements.