API from Google that performs image classification, optical character recognition (OCR), and other functions. Free within certain daily usage limits.
Image Processing or Image Analysis, terms often used for quantitative analysis of images, is a quickly growing part of Digital Humanities. One example area includes "Image Classification", the process of using machine learning to extract objects from an image (e.g. hat, apple, dog, boat). However, Image Processing is not limited to classification, but might also include analysis and visualization of image metadata, or Optical Character Recognition (OCR).
Image credit: blog post about Google Vision API, [link]
From the project website, "Photogrammar is a web-based platform for organizing, searching, and visualizing the 170,000 photographs from 1935 to 1945 created by the United States Farm Security Administration and Office of War Information (FSA-OWI)".
TensorFlow is a cross-platform library from Google that facilitates machine and training models. TensorFlow supports Image Recognition, and has some tutorials available.