Hi,
The path which is used is the upload folder, not the image folder.
That's why the relative path does not work.
When thumbnails are generated, it uses our Image Helper which would open the image from the upload directory.
The generator would put the thumbnail image in the same "relative" path but for the "thumbnail_100x100" folder (or other values for other thumbnail sizes). If you put a absolute path, I am not sure that it would create a right thumbnail relative path.
We are working on a new thumbnail generator for HikaShop 2.0.1, I will see if we can improve it.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.