A course on digital libraries and building digital collections.
Following the guide “Creating an Action for Batch Processing in Photoshop” by Sue Chastain to implement batch processing of images in photoshop. After following this guide, you could try to create a batch process to create large, medium, and thumbnail images as you did with imagemagick.
Sample image files for lab: http://ella.slis.indiana.edu/~jawalsh/teaching/z652/sample_images.zip