1) Exploit too much 2) Screw up in the darkroom 
• (v. t.) to subject (a plate or film) too long to the developing process. • (v. t.) To develop excessively;
To give more than normal the amount of development
O`ver·de·vel'op transitive verb To develop excessively; specif. (Photog.) , to subject (a plate or film) too long to the developing process. 
To give more than normal the amount of development. 
to develop to excess: to overdevelop a photograph; to overdevelop a waterfront area.