It apparently shows Amida Buddha welcoming the dying into the Western Paradise.
The painting type is called a Raigo.
Sorry to hear about your knee. Cross legged sittings are meant to provide a stable platform of support between both knees and the base of the spine. While one of these three is unable to be supported by direct contact with the ground, a bit of a balancing act ensues. Another cushion just under the suspended knee is the usual advice when folks really want a cross legged position to meditate in while they are trying to allow their ligaments to stretch to allow it.
Seiza or a chair are simply more appropriate for many bodies. When I have had to switch to a chair while recovering from injuries, the only meditative difference that I noticed was discovering how much of an ego investment I had when no longer "looking" as arduous a practitioner as my fellow peers. Oh what foolish beasts we can be.
I guess you could say that chair turned out to be the better teacher at that moment than the tenderly coveted hand made temple zafu that had my ass for decades.