Online Archive of California Not only California history, these collections are held by California institutions. Searching is very limited and you will want to add the word photograph to your topic term. Once you have results, limit to 'online items available.'
Calisphere Digitized images and documents from a variety of California universities, museums and archives. Some collections offer more photographic images than others. Overlaps the Online Archive of California.
Internet Archive Varied collections including images from a broad range of topics, countries and time periods.
Life Photo Archive Life Magazine was famous for its image-rich publications. Very little text was included with the photographs that were published, depending on the image to tell the story. Sorted by decade and by topic as well as keyword search.
Pageant of America Collection of photographs covering the US and North American continent from early discovery artifacts to the early 20th century.
Cartooning for Peace is from the United Nations and includes fairly recent cartoons from a variety of international sources on topics such as politics, environment, censorship and war.
The number of image collections by subject increases all the time. Contact me for help in finding what you need.
Using Google to Find Images
Google Images is one way to locate historical images but has some challenges as well.
There is no way to limit the search to primary sources.
You will find historical and modern images mixed together from sources ranging from hobbyist sites (Pinterest) to scholarly museum collections.
What you see in Google Images may not be the entire original image. Clipping a piece out of a larger image alters the context and meaning.
Do NOT cite Google Images as your source. You must follow the trail to the original digitized image source.
Check for permissions. Finding it on the internet does not mean you have permission to use. Most institutions allow no-fee use for educational purposes such as student papers, but there are some that do not (Getty Images for one.) Others require you to request permission to use and will generally grant for student use.
Here is a video on following a 'breadcrumb trail' in a Google Image search to a source you can cite. [adelitas example]