A conservative estimate of the number of orphan books as a percentage of in-copyright books across Europe puts the number at 3 million orphan books (13 % of the total number of in copyright books). The older the books the higher the percentage of orphan works.
When handling requests for using older film material, film archives from across Europe categorized after search for rights holders 129000 film works as orphan which could therefore not be used. Works that can be presumed to be orphan without actually searching for the right holders augments the figure to approximately 225 000 film works.
A digitisation project in the UK found that 95 % of newspapers from before 1912 are orphan.
Also, a survey amongst museums in the UK found that the rights holders of 17 million photographs (that is 90% of the total collections of photographs of the museums) could not be traced.
Anna Vuopala Assessment of the Orphan works issue and Costs for Rights Clearance P43
3 Million Orphan Books In Europe – EC Report Resource Shelf
Direct link to download the report PDF
Publishing Perspectives notes that the cost of clearing digital rights is often higher than digitisation itself and looks at a possible solution based on Norway’s collective licence for online access to copyright works. Concludes
The fact is that clearing rights — immensely complicated, difficult, and expensive — and not technology, remains the biggest obstacle to digitizing Europe’s libraries and making them available to a wider public.
Will Europe’s Three Million Orphan Books Ever Be Digitized?