Crosslinked organic porous particles are non-swellable in propyl acetate and have a crosslinked organic solid phase and discrete pores dispersed within the crosslinked organic solid phase, which discrete pores are isolated from each other. The discrete pores have an average size greater than or equal to 0.1 μm and the crosslinked organic porous particles have a mode particle size of at least 3 μm and up to and including 100 μm. The discrete pores can contain a marker material.