As the penis develops in-utero, the foreskin and the head of the penis develop with a bonding membrane between them called synechia. This membrane will not release for many years. As it does, the foreskin becomes retractable. This could happen anytime up to even the teen years (everybody is different). At birth, this membrane helps keep the foreskin forward to protect not only the urethra (where pee comes out) but also the still developing glans penis (head).
Prior to the excision (cutting off) of the foreskin, it and the glans must be separated. This is accomplished by inserting a blunt probe, usually forceps, under the foreskin, tearing it out and away from the glans. This would be as painful as shoving something under your fingernail to tear your nail away from the bed, accept, on the penis, a much more sensitive organ. As a result, the head of the penis itself is left a raw wound.
A complication of this step is that the two structures may not separate evenly. Just like when you peel a sticker from paper, sometimes the paper comes up too. Occasionally, some of the surface skin of the glans may be torn, leaving a pitted, or scarred area.
When the foreskin is finally removed there is a ring of tissue around the penis that is also a raw wound. Because everyone's penis and circumcision are different, the amount of skin left, and the looseness of that skin will vary. When the two raw wounds (glans and circumcision ring) touch each other, the body does not know the difference, and they attempt to heal together. This causes a variation of severity in deformation of the penis, from a simple skin bridge, where a spot of the shaft is attached to the glans, to major adhesions that cover the corona (ridge on the head).
To see other examples of this type of circumcision damage, please visit http://www.noharmm.org and click on Education - Photographs - Skin bridges.