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It depends on number of images you want to upload. And if you need to upload everything quickly I suggest you to use automated import services. Most of them give you a guarantee that everything will work fine. I have found one service. It is called file2cart. It will help you to upload images without errors and in a very short period of time. I’ve tried it a few times and I’m satisfied. Using this extension you can transfer your data from csv, xml,txt, xls.
So i think you need to check it out. I hope it will help you.