Yeshayahu Stengel (later Shacher) studied European and Jewish history at Hebrew University of Jerusalem.
His 1963 master's thesis was entitled Criticism of the Jewish community and Its Leadership in the Hasidic and Non-Hasidic Literature of Eighteenth century Poland—A Comparative Study (in Hebrew, 66 pages, 1964).
Shachar later became a junior research fellow at the Warburg Institute (University of London) where he worked on a doctoral dissertation under the supervision of professor E. H. Gombrich (which was finished 1967).
It was published in his main work: The Judensau: A Medieval Anti-Jewish Motif and Its History, Warburg Institute Surveys, 5 (London, 1974).
Later, a memorial volume commemorating his life and works was edited by Clare Moore in 1993: The Visual Dimension: Aspects of Jewish Art (Westview Press, 1993).