The Lesser Spotted Eagle (Clanga pomarina) looks very similar to the Greater Spotted Eagle (Clanga clanga) which also occurs in Greece (albeit more rare).
However, the Lesser Spotted Eagle is smaller and lighter in color (a distinct pale/dark contrast), while the Greater Spotted Eagle is slightly larger and much darker and uniform in color.
Adult Lesser Spotted Eagle have two diagnostic white "commas" on the wrist of the underwing (rather than a single one in Greater Spotted Eagle).
The Lesser Spotted Eagle prefers open woodlands, forest edges and low-intensity agricultural lands, while the Greater Spotted Eagle is more strictly tied to wetlands, lakes and marshes.

Lake Koroneia, Thessaloniki, Greece, 31 July 2017