What's So Difficult About Creating an Animation?

In our class yesterday we used our "processed images" to create the beginnings of a movie, better known as animations. I thought I had some great images that I had tweaked and processed through a program called foto flexer. For example I took a real life image of a flower and turned it into a cartoon. Then I took a picture of me from a trip to Jamaica and created a blue print of me drinking a beer. I also altered a picture of "real life" cabs rushing down the street in NYC to become a painting-like vibrant illustration.
Of course when we began constructing our animations yesterday I was so excited to see all of my "different" (being the key word) images become a movie.
I completed all the steps, transforming each image into a "gif" file and changing the speed of the picture so that the change from image to image would occur slower.
When I finished all of the leg work and finally played my movie I was shocked to find out that all of my pictures, rather than looking like an evolving movie, just piled on top of one another to look like a giant mess!
The step I missed somewhere along the line was this: THE PICTURES HAVE TO BE THE SAME SIZE AND SHOULD BE ALTERED IMAGES OF THE SAME PHOTO!. This was a key factor into why my first animation did not work. I felt a bit silly afterwords. If you think back to those "flip books" that when you turned the pages really fast the images on the pages of the book moved and looked like an animation. Why did this work? Because the images were all the same except for minute and minor alterations with each page.
Because this is an educational setting and not a professional movie making studio I posted "My First Animation Attempt" on my homepage with this link to help anyone who may have experienced the same mistake.
You can check out my new and improved "Cab Movie" otherwise known as "My Second Attempt at Animation" at the link below!