possible encryption

My school's website has a script that shows you your school picture. The script finds your picture through an "image_key" parameter. Below are a few examples of the parameter. Is this an encryption? If it is, could someone please tell me what kind of encryption it is and how I can decrypt/encrypt them. thanks.

image_loader.cgi?image_key=4RqaL*ujZhRWznlO5rjbaHaRmX5s7sBf
image_loader.cgi?image_key=pw**PuL*sAcrKtkw2Ae2do7HbIPEIAUY
image_loader.cgi?image_key=jiLOmgwaWhbHn*0MZXz*PbUyZ*KnzIsJ
image_loader.cgi?image_key=umTIf6E0BkEhRp*ACxLqqlh*p22J2mgl
image_loader.cgi?image_key=oJXJ5hIWHpLrXG6Ie4m0S0uyVF6*Dz44