Since Tidy Up is able to compare the data of the image representation1, excluding the metadata, when a search includes images and they are compared by content, it will prompt you to choose between a comparison of the entire file or of the representation data only (Figure below).
If the comparison of the entire file is chosen, the search will be faster but less accurate. The search by representation data only may report more duplicates, but the search will be markedly slowed down.
1) An image file is formed by two kinds of data: the EXIF metadata and the representation data. The former contains all the information about the image, such as date taken, camera model, GPS coordinates, etc., while the latter contains the data used to represent the images itself.