If you use a desktop/laptop, you can download a free program called EZ Thumbs and after you configure it, you can have it make a single pic or a whole folder of pics into resized images of a set size...whole folder would go to a preselected size and saved. It calls them thumbnails but you can select any size you want for the pic to come out...doesnt have to be small...

Link:
https://www.fookes.com/easy-thumbnails