A digital stamp, in mail or philately, is similar to a conventional postage stamp except it is resident on or in a computer; it can typically be downloaded and printed onto envelopes or packages by authorized individuals.

Some artistamp-issuing entities have issued "digital stamps", which have usually remained only pictures on a computer.

See computer vended postage.

Reference:

• http://www.guardian.co.uk/online/news/0,12597,1123533,00.html
• Royal Mail Launches Digital Stamp