Oil leaking from the crankcase cover

[Mr.Blue]

Hello everybody! I recently purchased my first bike, a used 2006 GZ250 from a dealer. However, I have begun to notice oil leaking on/in the locations in the photos. The oil does not leak when I park the bike and if it does it is minute but when I am riding and retrace my steps I notice that there is a large trail of oil following me wherever I go. I believe it may be the seals and am wondering for input from someone with more knowledge than I. In the location of the second photo the seal does seem to be coming off and there is a bolt missing as well so I believe that would cause the seal to loosen. However, when riding, I am losing leaving a significant trail of oil (in my 30 minute ride this morning I lost about a quarter of the oil in my engine). Does having a loose seal around the crankshaft have the possibility to produce such a spill or may there be a bigger problem? And, if it is just the seal, how difficult would changing them be for a new rider?

Thank you, Mr.Blue