How to extract image from sprite sheet without metadata?

I have a set of images that each has loads of smaller images. How do I go about extracting these images to use in my game?
I don’t have any JSON or other metadata about actual positions of images. Do I have to manually cut them out or remember coordinates of everything?

Or is there a less painful way to do this?

Here is the example of such sprite sheet.

25221-demon0.png

unity3d can cut it into pieces for you

but i use the 2DToolkit instead too