Our research in the field of bulk SI (semi-insulating) GaAs detectors for digital imaging has taken almost 20 years. We have optimized the process of detector fabrication and improved the detector quality in terms of its detection properties. We have obtained the energy resolution of 7.2% for 122 keV photons decreased to 5.3% by cooling the detector to 255 K. The typical charge collection efficiency of our SI GaAs detectors is between 85 and 88%. Besides, we were developing various X-ray imaging systems. We started with moving one single detector, where we obtained a spatial resolution of 500 mu m but the exposition period was of several hours. Later we prepared a digital X-ray scanner composed of 480 strip detectors in one line scanning an area of 12x15 cm(2) and obtaining the spatial resolution of 250 mu m. This fully homemade scanner shortened the exposition time to several minutes. Finally we have fabricated a two-dimensional system of 256x256 pixel SI GaAs detectors covering an area of 1.4x1.4 cm(2) suitable for Timepix read-out chip developed by the MEDIPIX2 collaboration reaching a basic spatial resolution of 55 mu m and exposition in the range of not more than a few seconds.