Scott is expecting his hard drive to fail soon, so he's been backing up his data. He has over 12,000 photos, and he knows that some of them are duplicates. Leo says that de-duplication is tricky because he has to preserve the originals while getting rid of the extras. If he's not careful, he could get rid of an original due to a false positive. So Scott will want an app that not only looks at the file name and size but actually deep dives into the data inside it.
Leo recommends Mind Gems Fast Duplicate File Finder. It not only looks inside the file, but it also has a close match feature. But just to be safe, before he de-dupes, he should backup everything at least once.