All the images here are available under the Creative Commons Attribution 3.0 unported license, commonly known as CC-BY-3.0.
This means you can do what you like with them, but they must be credited properly. If you want to reuse the images on the front page, that just means leaving the credit string in the bottom right corner intact.
The reason for this is that some of the source assets that are used to render these images require this. These assets must be credited.
If you render an image yourself using my tools, then you're at liberty to do what you like with them --- you don't have to release them as CC-BY-3.0 --- but remember that you are still bound by the attribution requirement of the source assets.
Please email me at firstname.lastname@example.org if you have any queries.