Proszynski was a member of the Warsaw Photographic Society from a young age, no doubt influenced by his family; his grandfather managed a photographic business in Minsk from 1839, and his father was an enthusiastic amateur photographer. Shortly after commencing his studies at Liege Polytechnic in 1893, he started experimenting with cinematography. There are claims that by the end of 1894 he had made his own apparatus, the Pleograf. By 1898, he had developed and demonstrated the Bio-pleograf. This apparatus (like Max Skadanowsky's first projector) used two films moving alternately, so that an image was always being projected, with no period of darkness between; an arrangement that was very successful in reducing flicker, but was too cumbersome to be widely adopted. Demonstrations in 1899 included some of his own films, made from a single negative. In 1902/3 the Pleograf Company was formed in Warsaw to promote his invention, and within a year or two a single-film model had been devised. In 1906 or 1907 he returned to complete his studies in Liege, taking his engineering degree in 1908. He continued working on the problem of reducing flicker, and was instrumental in promoting the three-blade shutter, which was a simple but important improvement in projection design. Shortly after he demonstrated this in Paris, it was adopted by the Gaumont Company and other equipment manufacturers.
By 1910 he had developed the Aeroscope (originally Autopleograf) camera, which used compressed air as a power source, enabling it to be hand-held. This went into production in England in 1912, first by Newman & Sinclair, later by F. Van Neck. It became very popular, particularly for aerial photography, and was used by film-makers for many years, including the nature and travel photographer Cherry Kearton, and newsreel and War Office 'kinematographer' Geoffrey Malins. Between 1911/12 and 1915 Proszinski worked in London with the Warwick Trading Company, and experimented with pneumatic synchronisation of films and sound disc. The Oko (Polish for 'eye'), an amateur camera/projector of novel design, used a 12 cm-wide film with the miniature images in rows of fifteen, which were scanned from left to right, giving twenty minutes of projection from only three feet of film. It was patented in 1912, but the war disrupted progress; in 1923 limited production started in Poland, but had ceased by 1925, by which time only about 100 examples had been made. The inventor stayed on in Warsaw; his later projects included the 'autolektor', a device for recording the text of books on sound film for the blind. In August 1944, Proszynski was arrested by the Germans and sent to Gross-Rosen concentration camp and from there to Mauthausen, where he died in March, 1945.