Thought for ya Jugo on the per style thing.
What if the delimiter was set per style?
Then as you describe it would only grab the images that started with that delimiter so if for example if you had the images
style_a_image1
style_a_image2
style_b_image1
style_b_image2
then you would set the delimiter for style a to "style_a" and similiar for style b
It may be completely off from how it would have to be done, just spitting ideas out from my insane noggin for ya as I know the style thing is giving ya a headache