Copier have black line through paper when copy

SOURCE: PIXMA MP780 Canon Copier skipping lines

Try cleaning printhead (google it you find it) make sure you attempt cleaning with Windex ammonia D (overnight solution)

If not you may have to replace Printhead (Plastic Box, cartridges snap into) sometimes the resistor will burn out.
1-800-828-4040 (Direct from Canon $31 + shipping)

If that doesn''t work contact www.usa.canon.com and find authorized printer repair. location. I am having same problem!!!

SOURCE: Single black line down center of newly copied page when using Auto feeder to copy

I had this same problem but after while it went away - so my solution would be to just keep using it, and perhaps it will solve itself.

SOURCE: Black line down the paper on copy mode. Ok in print mode.

There is most likely something on your scan glass that is blocking the scanner. Clean of both pieces of glass that are there when you flip open the ADF, or top cover. Try to copy again. If it is still there then there is either something on the scanner piece that moves back and forth to scan or one of your scan LEDs is burnt out and the scanner will have to be replaced.