Wondering how do I clip images to polygon outlines in a web map application based on OpenLayers or Leaflet? How can I limit web map users to see (visualize; qualitative) or query (quantitative) within the field polygons? E.g. user John has polys 1, 2 and 3 and user Mark has polys 7, 8 and 9. I want to limit John to just his polys and Mark to just his polys. I guess I can clip the images for each user and his polys, but if there are multiple users wanting to access the same images and polys, its redundant to copy the images to multiple users... Is there a programmatic way to limit this? Open source tools are preferred.