We can not directly add Publishing Images library from the list of libraries we have for that site. Though we can manually type and add it.
Using this library and using items’ link or whole item to image controll will not load images.
We can only load these images if we have url which ends with “file name.jpg”, “file name.png” or other image extensions.
Thus, instead adding Publishing Images library into the POwer Apps we can follow below steps:

1. create a list
2. add Hyperlink or Picture column named ImageLink
3. copy url of any of the image from Publishing Images library
4. use this list in Power Apps.
5. add Image control and in default property add ImageLink column.

These steps will allow us to display images from Publishing Images Library.