It's one of the Tussock caterpillars, but it would be very difficult for me to identify which one (of many) from one blurry image. They can resemble each other very much.

What is the plant you've found it on? Sometimes, that information can be useful.

It was on some iceberg lettuce.

If you're interested in a deeper ID of your caterpillar, I've attached a Google search of Tussock caterpillars of Australia. Many of the websites have good images for you compare with your caterpillar. You're in a better position to be a good detective than we are with that one picture.

A warning....tussock caterpillars can cause a mild skin reaction in most people. They have specialized hairs that can be very irritating. Handle with care.

Here is the HOSTs database for tussocks/Australia. Note the hostplants name column, very few if any herbaceous annuals such as lettuce. Suspect instead nearby taller shrubs or trees.

http://www.nhm.ac.uk/our-science/data/hostplants/search/list.dsml?PSpeciesqtype=starts+with&PFamilyqtype=starts+with&sort=Family&Family=lymantriid&Familyqtype=starts+with&Speciesqtype=starts+with&Genusqtype=starts+with&PGenusqtype=starts+with&Country=Australia&beginIndex=0&searchPageURL=index.dsml%3fPSpeciesqtype%3dstarts%2bwith%26PFamilyqtype%3dstarts%2bwith%26sort%3dFamily%26Family%3dlymantriid%26Familyqtype%3dstarts%2bwith%26beginIndex%3d30%26Speciesqtype%3dstarts%2bwith%26Genusqtype%3dstarts%2bwith%26PGenusqtype%3dstarts%2bwith%26Country%3dAustralia&listPageURL=list.dsml%3fPSpeciesqtype%3dstarts%2bwith%26PFamilyqtype%3dstarts%2bwith%26sort%3dFamily%26Family%3dlymantriid%26Familyqtype%3dstarts%2bwith%26beginIndex%3d30%26Speciesqtype%3dstarts%2bwith%26Genusqtype%3dstarts%2bwith%26PGenusqtype%3dstarts%2bwith%26Country%3dAustralia