A couple interesting markets looking for story submissions:
* Dark Chapter Press Flash Fiction Competition
1,000 words. Deadline: 23:59 London time, Jan. 30
Sub story based on picture and theme, "Explosion in the Alchemist's Laboratory." See above link for all details.
* Mental Ward - Experiments anthology - Siren's Call
4,000 words minimum. Deadline: March 1. Pay: $25
Stories must be in an asylum or mental ward and involve persons from the institution - staff, doctors, patients, etc. - performing an inhumane experiment. Tell what goes on behind closed doors; the things that are feared and what drives someone to do such things. See link for all details and description.
** Here's a good explanation on the Five Elements That Make a Good Horror Story for some inspiration.