While it's best to use original shots where you can, we need to be practical and draw on stock shots from time to time.
I've compiled a list of links to sites that offer images for free under the Creative Commons Licence. While free to use, do check what is required around attribution of the shot - the sites do vary in requirements, and sometimes there are both free and pay to use images on the one site.
Vintage and black & whites
Pond5.com is a random selection of older images, with famous figures and events included as well. It has a good search function and includes sounds and video in the mix.
Where as New Old Stock is exclusively old vintage black and white images, as well as ‘vintage’ posters, including interesting propaganda from the world wards.
One site to rule them all
Librestock is an aggregator site that brings in images from lots of different sites. It’s generally updated regularly, but as with all these sites, check that the license on the image is still free.
Because it is an aggregator, some of the images get used a lot, so you might want to dive into some individual photo stock sites that have a good variety (and also possibly contribute to Librestock).
There are so many handy tools to create video now, that throwing in a little stock video can really take things to the next level.
The following have some stock video for use under the Creative Commons License.
https://www.videezy.com/ - but check as sometimes it’s only for non-commercial use