CataloguePlus covers more than 20,000 images from our special collections.
The Allard Pierson image databases [Dutch interface only] contain digitised images from Allard Pierson, the collection of the University of Amsterdam. You can do searches by subject, creator, title, etc.
Startpagina Beeldbanken contains links to a great many Dutch image databases.
For older pictures there are image databases of archives. At Europeana you can find digital images from the collections of European museums, libraries and archives.
Google Search by Image enables you to search with an image by clicking the camera icon.