no reason in theory why an IQ test delivered on paper couldn't also be delivered online - though the result couldn't likely be used for anything other than just information for the person taking the test. A site purporting to offer you a certificate(mentioned earlier) etc.. is inherently dubious/pointless as that poster pointed out.
then again even 'official' IQ tests are of fairly limited use anyway and joining something like mensa is pretty pointless too... they mostly tell you how good you are at IQ tests (a skill that you can improve on with practice) - they have some relation to your analytical ability, abstract reasoning etc.. but they're not necessarily a measure of 'intelligence' - which varies in definition anyway and generally isn't going to be useful to summarise in a single parameter
then again even 'official' IQ tests are of fairly limited use anyway and joining something like mensa is pretty pointless too... they mostly tell you how good you are at IQ tests (a skill that you can improve on with practice) - they have some relation to your analytical ability, abstract reasoning etc.. but they're not necessarily a measure of 'intelligence' - which varies in definition anyway and generally isn't going to be useful to summarise in a single parameter