Representations of images, in general, belong to three probabilistic families, developed for different regimes of data and tasks. (i) Descriptive models, originated from statistical physics, reproduce certain statistical regularities in data, and are often suitable for patterns in the high entropy regime, such as MRF, Gibbs and FRAME. (ii) Generative models, originated from harmonic analysis, seek latent variables and dictionaries to explain data in parsimonious representations, and are often more effective for the low entropy regime, such as sparse models and auto-encoders.