If you find an image on a blog or website, you should try to trace it back to the original publication or archive where it can be found.
The easiest way to assure proper attribution is to start your search with this goal in mind. Try searching historical newspaper databases like ProQuest Historical Newspapers or image repositories like JSTOR.
If you already have an image and you are having a hard time finding the source, Google Reverse Image Search might be an option. But keep in mind that this is only a tool for finding more information about your image and it rarely leads to the primary source itself. Additionally, downloading the image and looking at the information associated with the file or right clicking on the image can sometimes offer more clues about where to find its origin.