Striped flags alternating green, white and red colors were commonly observed as used by Algerian ships - either peaceful or warlike ones; while the introduction of the three crescents seems to point to the regular Ottoman Navy. On the other side, the use of flags showing a skull and scimitar, or an individual's portrait, were also frequently reported.
Source: «Flags of The World» (FOTW) website:Algeria, Miscellaneous flag reports, late 18th - early 19th century
Sizes: swallow tailed ensign W8 x L20mm, rectangular ensign W12 x L18 mm, mast flag W8 x L12 mm, jack W6 x L9 mm, pennant W4 x L48 mm.