The two conditions are clinically different. For a haemorrhoid, you will expect a soft swelling at the anal region. The haemorrhoid may be tender if it is acutely thrombosed. A thrombosed haemorrhoid will appear as a lump, protruding from the anus. It is usually dark blue as the blood vessels are swollen.
Haemorrhoid swelling happens due to an increase in pressure in vessels, therefore causes it to increase in size. Haemorrhoids lasts for a couple of days and recur frequently.
Meanwhile for a fissure, you may just feel a skin tag. The fissure is always tender. These fissures are tears of the mucosal lining of the rectum. It causes pain during and/or after your bowel movement. Often, it also accompanies with a throbbing pain.