On reddit there's a photoshop battle that's often humerous. Also a great excuse to learn.
If you're completely new to digital image editing then you may want to start with gimp. It is a free tool that should have everything you need to get started. If you're willing to invest then you might enjoy pixelmator too.
Tutorials are aplenty on youtube.If you want to commit to this idea, consider reminding yourself via dearme.email.
There's some great examples on the internet; there's a couple who demonstrates how to use a green screen with a cat, a collection of photoshopped cat faces, dogs that look like food, an owner masking his dog unto famous people or this man who turns his dog into a giant. You can also keep it simple and just record how animals react to objects.
It's a great excuse to learn some photoshop skills or to learn how to do some digital video editing and there's many ways to make your pets famous. Just make sure that whatever you do with your pets, they enjoy it too.If you want to commit to this idea, consider reminding yourself via dearme.email.