It is shown that recentering, selecting, and adding up sharp short-exposure images obtained with a photon-counting detector working in time-resolved mode can yield a gain in angular resolution better than a factor of 2. A cross-correlation selection algorithm, appropriate for faint and extended objects, is developed and compared with other image sharpness criteria. The limiting magnitude of the technique is 15 under normal conditions (seeing = 1 arcsec). Selecting the moments of best seeing during the night improves this limit by two or three magnitudes. Thus, a large number of extragalactic objects can be easily imaged with a resolution of a few tenths of an arcsec. Results for a sample of bright active galaxies are presented.