You have to connect the iPad to the Mac and deselect the photos in the Photos tab of iTunes and follow that with a sync in order to remove the photos.
Connect the iPad to the Mac and launch iTunes.
Select your iPad from Devices in the upper right or in the left sidebar of iTunes, if the sidebar is enabled.
Click on the Photos tab in the iTunes window on the right.
Uncheck all of the albums and videos that you want to remove under the Sync Photos from heading.
Click on Apply in the lower right corner of iTunes.
If you want to remove all photos, uncheck the "Sync Photos From" heading and then click on Apply. If you can't see the sidebar, go to View>Show sidebar from the iTunes menu at the top.