In SliderDock, it's possible to change every image of the dock.
changing SliderDock theme :
To do so, right click on the IconSeeker, select "dock settings" and go to the "theme" tab :
You should see this :
On this screen, simply click on any image and select a new one.
changing an icon's image
Right click on the IconSeeker or any other icons and select "icon settings".
On this screen :
Click on the image and select a new one to replace it.
compatibility with other docks and themes + searching for new images
SliderDock is compatible with others dock themes and icons. Although the application comes with a limited amount of images, it's fairly easy to find new ones to customize it in any way you want.
Many websites offer free images to customize docks.
For example the websites DeviantArt.com possess a huge library of images.For example simply search for : "Recycle Bin icons" which return multitude of icons to choose from.