iPhoto duplicates issue
Hey guys I have been using iPhoto to transfer photos and videos from my iPod and iPhone to my MacBook Pro. To preserve memory what I have been doing is importing pics/vids using iPhoto and then drag and dropping them into folders I have created on my desktop to keep organized. I then transfer these folders to my external hard drive and delete them from my MacBook to save memory. Recently I noticed my memory is getting lower and videos and images are still viewable in my iPhoto recent imports tab. I would like to know if there a way to prevent iPhoto from keeping duplicates in its folder after I drag and drop the files to my desktop folder? Can I scan my hard drive and easily find and delete duplicates using finder? And lastly, if I were to use the photos program instead of iPhoto would I run into this problem again? Thanks in advance for the info!
MacBook Pro (13-inch Mid 2012), OS X Yosemite (10.10.5)