A system and methods are disclosed for training a machine learning model to identify constituent images within composite images. In one implementation, a composite image is generated, where the composite image comprises a first portion containing pixel data of a first constituent image, and a second portion containing pixel data of a second constituent image. A first training input comprising pixel data of the composite image and a first target output for the first training input are generated, where the first target output identifies a position of the first portion within the composite image. The training data is provided to train the machine learning model on (i) a set of training inputs comprising the first training input and (ii) a set of target outputs comprising the first target output.