How did I create this collage?

This may not be an iPhoto question, but if not, I need to know. Over a year ago I somehow created the collage below. I was sure I used iPhoto to do this, but now I can't find the features I used within iPhoto.

The software automatically sized the photos to fit. I have some other photo software kicking around, but I use Apple software 99% of the time, so my poor memory isn't helping.

If this wasn't done within iPhoto, does anyone recognize the template or can suggest what I might have used? I like the result and want to use it again.

Just letting me know that I couldn't have done this in iPhoto would help.

Thanks.

Charles