Always pay attention to the conditions to use an image.
There are a number of websites which provide press photos, such as Reuters or LIFE.
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. Startpagina Beeldbanken contains links to a great many Dutch image databases and archives.
Google Search by Image enables you to search with an image by clicking the camera icon.
Useful websites to find images free from copyright are Pixabay and Free images. On Flickr you can filter for “all creative commons” to find (partially) free images.
The Allard Pierson image databases contain digitised images from Allard Pierson, the collection of the University of Amsterdam. You can do searches by subject, creator, title, etc.
CataloguePlus covers more than 20,000 images from our special collections.