I have currently ~20 000 photos in my photos library. Most of them are snapshots so I would like to reduce the size of the library from currently 90 GB. To that end I would like to delete all the crappy pics I have. I plan to do this from my iPad during the next couple of weeks. Step one would be duplicating the entire library to have a save backup with everything (at home and at dropbox). How do I most efficiently duplicate the library? In finder or through photos? Step two would be simply scrolling through 20 000 photos on my iPad whenever I have time and simply delete every pic that is not interesting. I hope to get rid of 75% of the pics this way. I have my Photos library in iCloud so the deletion process could be done of the phone, the iPad or the Mac. Is that correct? Has anybody done something similar? Any input on my plan to do this and any info about pitfalls would be helpful. Thanks!