I see two possible ways to accomplish what you want:
1.- Split your image in two parts matching to the size of your table cells (using photoshop or any other image manipulation software), then use each image for its respective cell.
2.- Use the same background image for both cells (<td>) but in the second one adjust the offset of the background using the
background-position CSS property.
Example:
<td style="background-image: url('picture.jpg'); background-repeat:no-repeat; background-attachment:fixed; background-position: -100px 0px;">
In the example, I am assuming that the first <td> or cell has a width of 100px, this way, when I set the
background-position CSS property of the second cell to -100px, the background image will be moved 100 pixels to the left, starting, hopefully, right where the background of the first cell ended.
I hope this is helpfull.
REGARDS