First, what kind of vehicle is this on? Without that known, there is usually only two reason to have a leak at the oil filter:
1 - oil filter gasket itself, for one reason or another - if the filter gasket was not lubricated with oil before it was installed, or the filter has been on the vehicle for a long time, it can stay stuck on the vehicle when the filter is removed for an oil change - when a new filter is installed, the gasket on the new oil filter makes contact with the old gasket instead of the engine, and leaks - this is very, very dangerous situation because the oil can be lost in a matter of a minute if the old gasket breaks loose - the engine most likely would be ruined before you could get off the road if driving at 70 mph... Pull the filter off, make sure the old gasket is not the problem, clean off the sealing surfaces on the engine and the filter, oil the filter gasket with clean motor oil, and re-install filter - tighten 3/4 turn once filter gasket makes contact... If still leaking, install a new filter of different brand... 2 - if this is on vehicle that has an engine oil cooler, (usually an option or part of a trailer towing package) there is a o-ring at the oil cooler/filter adapter, where the oil lines going to the oil cooler are installed. The o-ring gets hard as time and heat degrades it, and starts leaking - sometimes, a lot... To fix, buy a new o-ring ($6 or so), remove oil filter, remove the bolt in in the center of the oil cooler/filter adapter, pull away from engine only enough to completely scrape out o-ring out of the grooves, install the new o-ring, re-install center bolt, and the oil filter. It is hard to scrape out the old o-ring, but a lot cheaper than adding a quart of oil after every trip... 3 - Always check for leaks when replacing the oil filter - even if there has never been a problem - only takes one time to have a mess to clean up, or an engine to replace... 4 - Check to see if the leak could be comming from the oil pressure sending unit, located above the filter on the 4.0 L, it leaks on the filter and runs off.