The ImageShow.Viewer class is the base class for viewers. When creating a new instance of this class, it mus tbe registered with ImageShow.register() before it can be used. The register() function takes the viewer as an argument, and also the order which  determines whether to prepend or append the viewer to the global list of viewers. A positive integer appends while a negative integer prepends.
```python
ImageShow.register(viewer, order)
```

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The ImageShow class is used for displaying images to the system's screen. Images are displayed through objects called viewers. There are a number of default viewers in Pillow, so creating new viewers is not necessary for showing an image.
Showing an image requires the show() function.
```python
ImageShow.show(image)
```
show() returns true if a suitable viewer was found.

ImageShow Class (Pillow)

https://pillow.readthedocs.io/en/stable/index.html

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