how imageset is to be used?

I can't use the function imageSet.I made a folder named 'imgfolder' with two subfolder named s1 and s2 respectively with 5 JPG image each.When i write the code faceDatabase=imageSet('imgfolder','recursive'); I found error Undefined function 'imageSet' for input arguments of type 'char'. Error in Untitled (line 1) faceDatabase=imageSet('imgfolder','recursive');