Multiple Exposures

One of the things I am looking at now is photo editing.  I don't have Photoshop or a similar program, just the free downloads of Irfanview and Picasa.  With these two programs, I have discovered how to work on multiple exposures.  First of all I tried to get complicated, putting four photos into this one of Rundle Mall.

Rundle Mall, with the bronze pig, the fountain, tree and the "Malls Balls", all layered together.  A bit too much.

So then I simplified for this, showing my cat overlaying the marine aquarium - just 2 photos.