What are these lines on the fuselage of a 747? Have a look at this picture:                                                  

It's from Airliners.net (though I've modified it a lot) and shows some lines on the fuselage. What are they? Are they Lightning Diverter Strips like in this question ?
No, they are just the boundaries between skin panels. See below for a picture of the 747-8 fuselage during assembly.

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Boeing 747-8 front from side (picture source)

And this is how the panels for the cylindrical section look like before they are joined:



Boeing 747-8 fuselage panels. The original picture (source) is named "wing panel skins", but these are really fuselage parts.