We participated in the GBIF digitization symposium at the Swedish Museum of Natural History where various natural history museums had met up to discuss the problems and possibilities of mass digitizing their collections. We were there to advocate that the digitised material be made available under free licenses and clearly marked as such.
Herbarium GB is currently digitizing its collection of herbarium sheets. They are intending to make these available but had not thought of the need for a clear license.
Naturalis (in the Netherlands) have released their digitized collections freely but are currently building a new portal for displaying their material. Once this is up it will be worth making sure the license is compatible with Wikimedia and look into including the material with species articles.
GBIF is the portal for data on biodiversity. They are pushing for clearer (and free) licensing from their participating organisations.