Extract Images from Photo Libraries
Brute force extracting photos form a photo library should not be a common task as library apps have civilized ways of doing it (File->Export). However you may want to do it.
File Juicer can extract photos from Photo Libraries, ignoring all databases and structure. This means that no matter the app which made the library you can pull the images out.
Normally File Juicer is set up to extract all it can recognize in the preferences. If you are extracting from a photo library and you are only interested in images formats, you can improve speed by unchecking the formats you are not looking for
Thumbnails and Previews
If you extract everything from a photo library you will likely get a lot of duplicated photos. This is because photo library apps generate low resolution version of the images to quick display when you browse the library.
Previews and thumbnails are usually small files compared to the original images.
You can sort images by file size in Finder to concentrate on the ones you are looking for.
Since thumbnails and previews are derived from the originals, they can be out of sync or leftovers. For forensic search this can reveal photos which may been deleted from the library. Since photo library apps clean these out at unknown intervals the reliabliilty of this is low.