What does that option do? And how it is different from Hide safe processes?
I believe that "Hide safe processes" will show all files that are not whitelisted. This will show those that are found to be suspicious or malicious by Comodo while also showing all processes that are simply unknown.
"Show only unsafe images in memory" will only show you the processes that are found suspicious or dangerous by Comodo. It will not show those that are simply unknown.