One survey of his false postmarks identifies 200 town names and almost 600 distinct cancellations, most applied to relatively inexpensive German stamps from the first half of the twentieth century. In September 2006 he was sentenced to four years of probation.
- Philatelie, November 2006.
- Stamp Magazine, February 2007, page 9.
- English-language article and list of Blüm's forged cancellations
- German-language site with extensive listing and examples of the forged cancellations
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