For an oil filter to leak...that would have to be VERY tight
As mentioned, the easiest way to find the leak will be to clean down the area and run the car a bit. Looking and observing where the leak begins.
From the bottom up the possible leak points are: Pressure areas are more likely to leave drips, non pressure will usually be more of a slow seep.
Oil pan (non pressure)
Oil pressure sender (pressure)
Oil filter adapter gasket (pressure)
Timing cover gasket (non pressure)
Valve cover gasket (non pressure)