President John F. Kennedy and First Lady Jacqueline Kennedy Attend Ballet Folklorico Performance, Mexico City, 1962. ST-C1-11-62. Used with permission, John F. Kennedy Presidential Library and Museum.
Whenever possible, search a reputable collection for original, high-quality scans. You are more likely to find accurate information as well as usage guidelines.
A good quality site, such as university, museum or special collection archive, provides basic information such as artist/photographer, date and location.
In addition, you may find helpful notes or description to place the image in historical context. Do not use this information as your secondary source as it will not have gone through the rigor of peer-review, but do use it as a 'launch pad' to understanding your image, its importance, and application to your historical topic.
Finding Images Using Google 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Do NOT cite Google Images as your source.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.