Image Resize Rename

The Question:

What file performs the resizing and renaming of images in wordpress 2.5?

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More Info (If you care):
I am using wordpress 2.5 with the recycled canvas template. When I upgraded to 2.5 I noticed that the template no longer recognized thumbnail images. Upon investigation I found that the newer wordpress saved my images as example-150×150.jpg instead of the previous example.thumbnail.jpg.

I see many options for attacking this problem; however, I do not want to search through a bunch of files and classes. If I could set the renaming of images back to .thumbnail. jpg it would solve all my problems; when I renamed the 150×150 files in my upload directory to .thumbnails it worked.

So where is the image resize and renaming file in wordpress 2.5?