Image associated with an object

Hi, I’m doing the Snowman-tutorial.
The trees are associated with an image that I have put in the same directory than the blend-file. When I render the file in blender, the trees appear with the image and that is correct.
Now, when I export the blend-file to x3d-file (which is in another directory), I also copy the related image file (.png) to the directory of the x3d-file so that it is reachable. The problem is that when I open the x3d-file with IE or Firefox, the trees appear without the image, that is, they appear simply white.

How can this happen?
I’d like to have some advice.

Thank you very much!