How can I get all the file in a fold in a web application?

I publish my web application in tomcat server,in a picture fold I set it as anonymous access,so everyone can get the picture according to its name,such as http://domainname/picturefold/abcdefg.jpg.Now I afraid that if someone know all of the picture uploaded in a flod called picturefold,but do not know the real name of the file,Whether he can loop all my picture file or not?