You want to add a signature to checks you print from QuickBooks Desktop.
You can create a signature image by signing a piece of paper and then scanning it and saving the scan to a file.
Your signature image should have an 11:3 aspect ratio (11 width and 3 height). It will be sized to fit into a a 2-3/4 inch wide by 3/4 inch tall space and placed directly above the signature line on Intuit-supplied checks.
Be sure your signature file is in the correct file format. QuickBooks accepts almost any image file format, including BMP, JPEG, PNG, and TIFF.
If you use QuickBooks user names and passwords, the signature file is stored by user name and company. If you do not have multiple user names and passwords, the Admin is the implicit user.
IMPORTANT: The Signature feature is not available for Wallet checks.