Just place files in site/modules/PixlrEditor/ folder and install PixlrEditor module. After that each FieldtypeImage field should have buttons to image editors.
You can enable/disable chosen image editor in PixlrEditor module settings:
Available editors:
- Pixlr Express
- Pixlr Editor
Probably works well with inputfield Repeater.
Not tested with Thumbnails module. It does not work on localhost. Pixlr webservice must have the ability to download images from your server.