Hi,
There isn't an option atm to disable the screenshot feature through the web ui however, if you trigger your build through the use of the studiocli on the appliance you can.
Here is an example of how you would do it from your console prompt:
studiocli --createbuild --noscreenshots --profile /opt/vmware/var/lib/build/profiles/Ubuntu12.04x64.xml
Substituting your profile obviously.