In most cases a bipedal character's posture can be tagged. I've included common options here, but there are edge cases not included here and more-detailed tags in the tag-group poses. These tags are not always mutually exclusive and in some cases, like close ups, none may apply.

Tag Options:

1. Standing A character upright and supported by their legs and feet
2. Sitting A character supported by the buttocks or thighs where the torso is more or less upright.
3. Reclining: A person who is sitting but lounging backwards, often supported by their arms or a raised surface.
4. Kneeling When a character's knees touch the ground or other surface beneath them.
5. Crouching Resting only on the feet with bent knees.
6. Straddling To stand or sit with a leg on each side of something. Especially useful in cases like cowgirl_position where kneeling/sitting/crouching can be unclear.
7. Lying When a character is more or less horizontal and supported along its length by the surface underneath.
8. Leaning Forward When a character bends forward at their waist, but not so far as to make a 90 degree angle.
9. Bent Over When a character is leaning over at a right angle with their back bent and legs roughly straight.
10. All Fours When a bipedal character (not characters who normally stand on four legs) has both sets of limbs resting against the ground.

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Note that some of these tags can apply to Quadrupeds but the definitions would all apply differently and things are much less clear, so I've (tried to) restrict the images to only those including bipeds.