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The key aspects of a new method, bubble-image barometry (BIB), which can measure both pressure and velocity, are described. BIB extends correlation-based particle-image velocimetry techniques to provide simultaneous pressure and velocity measurements over a global domain. The particles used in BIB (gas bubbles) serve two purposes: (i) they are small enough to track the flow and serve as tracers for the velocity field; and (ii) they behave as local pressure sensors by changing their size in response to the instantaneous pressure field. The present work explores the theoretical and practical issues involved in BIB by first introducing the relation between the bubble-image size and its spatial correlation function. Next, computer-generated bubble images are used to investigate the feasibility of the technique. Finally, a pressure-chamber experiment, wherein microscopic air bubbles are generated and used as tracer particles to measure pressure, is presented. Results obtained from the experiment show that BIB is a viable technique for a certain range of bubble sizes.