Digital imaging has traditionally been enabled by single-crystalline photodetectors. This approach typically either mandates the use of silicon as photon-to-electron converter or requires a hybrid-integrated solution. In contrast, solution-processed optoelectronic materials offer convenient integration of light-sensing materials atop an electronic readout circuit. Colloidal quantum dots offer particular advantages, combining solution-processing with the spectral tunability afforded by the quantum size effect. Here we review recent progress in solution-processed quantum dot photodetectors and their application in future imaging systems. We focus on progress towards high responsivity (photon-to-electron gains exceeding 1000) and sensitivity (normalized detectivity D* ~ 1013Jones) in the visible, the near infrared, and the short-wavelength infrared. We also highlight the achievement of solution-processed photoconductive photodetectors combining photoconductive gain and temporal responses faster than 30 ms, devices therefore compatible with video-frame-rate imaging. We conclude with a discussion of recent colloidal quantum dot photodiodes having megahertz bandwidth and detectivity of 1011Jones.