IIRC, Bagginsbill has stated that he can use Poser's nodes to do anything except apply a proper soften or blur effect to an image. The old Castle Poser website, however, had a shader setup to blur an image using a noise node. Unfortunately Castle Poser seems to be offline, and the snapshot at the internet archive doesn't include the images showing how to set up the shader.

The basic idea seems to be to plug a noise node (or suitable substitute) into the U_Offset and V_Offset inputs on your Image_Map node. Varying the values of the Offset inputs and the min and max on the noise node allows some measure of control. The result isn't really a high quality blurring effect, as one might expect from an image editor. I'm not sure whether Poser can do any better.

Castle Poser at the Internet Archive is here: https://web.archive.org/web/20161119180102/http://castleposer.co.uk/articles/shader_blur.html

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Cage can be an opinionated jerk who posts without thinking.  He apologizes for this.  He's honestly not trying to be a turkeyhead.

Cage had some freebies, compatible with Poser 11 and below.  His Python scripts were saved at archive.org, along with the rest of the Morphography site, where they were hosted.