Large background image, should I cut it?

I'm making a sidescroller platformer game, with a really long image as part of the level background. I'm putting the image on a large plane in the scene. Should I:

a) Cut up the image into several pieces that can be culled by the engine? I'm having trouble lining them up without a little line showing where the pieces join.

b) Leave it as it is, as one big plane?

c) Some other solution?

Well your best bet is to try both and profile them.

My guess is if you are using a single 4096 length image (max size for a texture on most cards) then there is no point cutting it up. The gpu will clip the polygon to the screen anyway so there should be no performance penalty at all.

If however you are already using multiple textures to get a length greater than 4096 then it may be beneficial, though more in terms of memory management than performance.

As for your lines where there are joins you should check that texture repeat is set to clamp and maybe use point filtering.