1. The jar (in your attached zip)  did not contain any compiled java class file.
2. The first java code is
package com.jhlabs.image;
It means that ConvolveFilter.java should be under com\jhlab\image directoory

public class ConvolveFilter extends AbstractBufferedImageOp {
It means that , AbstractBufferedImageOp.java is also required,
and AbstractBufferedImageOp.java need to be compiled before you can compile ConvolveFilter.java

When AbstractBufferedImageOp.class and AbstractBufferedImageOp.class are available.
Those files need to be packed into a jar file.

I found the filter.jar which contains all the filter at that web site.
Use it in the EJS ,remember to add import [b]com.jhlabs.image.*[/b] in the option page ,
and it should work now.