Licensed for reuse is a fancy way of saying that the person or organization who took/owns the image is happy for other people to use it as they see fit.
You can find images like this in two ways:
Search settings to find free blog images
The first is to change your search settings. To do this in Google for example, you should go into the settings menu. You find that menu by clicking on an icon that looks like a gear, here you choose advanced search, then usage rights drop down menu. There you can choose the option safe for reuse. This will ensure any images that are returned by the search enging are licensed for reuse.
The second method is much more straightforward, and it is the one I prefer. There is a website called Creative Commons. You can find it at https://search.creativecommons.org/. Once you are there, you choose the file type you want, and the search method. For example, you may choose Image and Google. Type in what you are looking for and hit search. It will show you all the images Google found that are reusable.
Using images which belong to someone else without their permission is illegal and immoral, so use either of the methods above and you can rest easy you’re not breaking the law or denying someone an income. And if you don’t like what you find, you can consider companies that sell images to reuse, like Getty Images.