Hi Luoy,
Well I tried to both attaching a image to a regular post and a custom post (slider) and neither work. The image will not show up in the slider and although I can click on the area it still brings me to a page and a blank area were I can click to the URL I want. I'm not sure why the image won't display and why I can have it click to the URL I really want it to direct to.
I've added you as a user to the site and put the details in the private area.
Good luck and thank you.
Sean