If you have ran a scan and no duplicates are found, don't worry. You either genuinely don't have any duplicates, or you need to tweak the criteria a little.
Common settings which can cause no duplicates to be found are:
Subfolders not being scanned. Are you scanning the subfolders of the input folders you have listed in the 'Folders to search' list? Be sure the 'Scan subfolders' column is set to 'Yes'.
System folder being ignored. Are you trying to scan a folder/subfolder which has a Windows 'System' attribute? Uncheck the 'Protect important system folders' settings in the Options drop-down menu. Always be careful not to delete system files unless you are sure you don't need them.
File filter restrictions. Check your file filters on the 'Search criteria tab'. Generally you want to scan everything (*.*) and exclude nothing.
File size/date restrictions. Check you don't have any file size or date restrictions in the Criteria tab. Try 'Any size' and 'Any date' if not sure.
Restrictive criteria. Make sure your search criteria isn't too restrictive. If searching by content, you don't generally need 'Same file name' or 'Same created / modified date'. If you have 'Same created date' checkmarked this won't generally find copied duplicates as they usually have different created dates.
Other folder settings. In the 'Folders to search' list make sure that 'Scan against self' is set to 'Yes' if you want to find duplicates within that folder. If 'Master' is set to 'Yes' then bear in mind that only files that duplicate any folder with the 'Master' flag will be shown.
Duplicate pictures not found. Be sure you are running in 'Image mode' to find similar images. Otherwise only exact duplicates (same image, tags, etc) will be found.
For Image Mode
This mode finds similar images. Supported image types are:
Any other file types are ignored in this mode. The program doesn't currently support RAW formats used by some cameras. (This is planned for a future release).
For Audio Mode
Supported file types are:
.mp3 .ogg .wav .wma .ape .flac .m4a .m4p
Audio mode (Match audio tags) relies on your files having been tagged with song title and artist information as a minimum. These tags (ID3) are usually created by the audio download or CD-ripping program (e.g. iTunes).
