You can have an infinite number of tiles on the X axis. But the Y Axis must only have a maximum of 3 tiles. Heres an example of the picture file:

[] = Tile or Picture


[][][][]... Infinite
[][][][]... Infinite
[][][][]... Infinite

Notice that there are 3 tiles going down. That is the maximum but you can have an infinite number to the right. Also the tiles must be 32 by 32 Pixels.
