**Core Concept**
A true bruise, also known as a contusion, is a type of skin injury caused by blood leakage into the surrounding tissue due to blood vessel damage. The characteristic appearance of a true bruise is often used in forensic medicine to differentiate it from artificial injuries.

**Why the Correct Answer is Right**
A true bruise typically has an irregular shape with regular margins, which is due to the bleeding into the tissue spaces. The bleeding is usually from small blood vessels, and as the blood accumulates, it forms a pool that is surrounded by a clear boundary where the blood has not yet leaked. This clear boundary is what gives the bruise regular margins. On the other hand, artificial bruises often have a more uniform shape and irregular margins, as they are created by external force or manipulation.

**Why Each Wrong Option is Incorrect**
**Option A:** Round shape, irregular margins is incorrect because a true bruise is more likely to have irregular margins due to the bleeding into tissue spaces. A round shape with irregular margins is more characteristic of an artificial bruise.
**Option C:** Swelling of surrounding area is incorrect because swelling is a common feature of many types of injuries, not just true bruises. While swelling may be present in some cases of true bruising, it is not a reliable feature to differentiate true from artificial bruises.
**Option D:** Erythema of surrounding areas is incorrect because erythema, or redness, is also a common feature of many types of injuries. While some true bruises may have erythema surrounding the bruise, this is not a reliable feature to differentiate true from artificial bruises.

**Clinical Pearl / High-Yield Fact**
When examining a potential bruise in a forensic context, pay close attention to the shape and margins of the bruise. A true bruise is more likely to have irregular margins, whereas an artificial bruise is more likely to have regular margins. This can be a useful clue in determining whether an injury is genuine or fabricated.

**✓ Correct Answer: B. Irregular shape with regular margins**