how to make repeating pattern from image

I have about 200 pictures with 200px in width and 150px in height.What I want to do is to create images with 1000px in width and 750px in height which is filled with repeated pattern by those pictures. For example I want to make this picture with one of those 200 pictures and save the new image name with the same image name from the one That I have used as pattern.How can I do so?