A method for processing images of animals obtains first training data, which includes first images of animals and first annotation data including first location data for predefined feature points on at least one animal in each image in the first images, and trains a first machine learning-based model (MLM) by use of the first training data to generate a first trained MLM. The method obtains second images of animals, operates the first trained MLM on the second images to generate second annotation data comprising second location data for the predefined feature points on at least one animal in each image in the second images, and aggregates at least a subset of the first and second images, and a corresponding subset of the first and second annotation data, into second training data, which thereby is expanded in relation to the first training data.