The recovered images may seem duplicated at first sight, but they are not absolutely identical. The size is different. This behavior is caused by the fact, that some JPG or TIFF images contain a preview inside the original picture. If this preview is binary and stored in the beginning of the file, Disk Drill will recover it as a small separate image.
You may be able to filter out the smaller images by adjusting the settings to filter out small file sizes. Try clicking on the drop-down menu next to Over on the filter bar and changing it from 0 KB to 128 KB (or more).