How can I light picture frames from the floor?
If you have the room on the floor, then you can get a floor mounted track style fixture.  These have a weighted base with the transformer in them to make them harder to knock over or move.

The only downside of using these are;


If they accidentally get moved into a couch or something like that it could become a fire issue.
If you cannot move it out from the wall because of restrictive space you might end up with a lighting technique called wall grazing.  This would cause the bottom of your frame (if it is a traditional wooden frame that stick out past the cloth itself) to cast a shadow across the painting.


The upsides are;


The lamps used have various beam spreads and wattages available for use.
LED's are made to be retrofitted into these by only changing the lamp.
If it works out you don't have to get on a ladder and hang track lighting.


I've seen renters (don't know if you are or not) hang track lighting and use something to hide the wire and just plug it into the wall and use a plug in dimmer to control the lights.  Then when they move they take it away.

The picture came from here.  Good Luck!