Knot drawings from Wikimedia Commons: bowline by Hella, adapted by Tescobar (CC BY-SA 3.0);
figure of eight, reef knot, sheet bend and rolling hitch by Lucasbosch (CC BY-SA 3.0);
round turn and two half hitches by Stephan Brunker (CC BY-SA 3.0);
clove hitch by Sawims (public domain). All other pictures are SailChecker's own.