I have discovered that a number of files on the NAA web site that previously had digital images have had them withdrawn by the National Archives of Australia Melbourne office.
The Item Details description states "Visibility and availability indicators - Digital image withheld"
The files I have noticed are from Series B357 and numbered
191 - Aboriginal Welfare Board field notes Western district genealogies
192 - Aboriginal Welfare Board field notes - Murray Valley, survey of Aborigines, June 1961, families
193 - Aboriginal Welfare Board field notes -Wimmera and Gippsland, genealogies
198 - Aboriginal Welfare Board field notes - genealogy
Digital files were previously available. No reason is given for the removal.
Indexes to Series B357 Items 192, 193 and 198 are available here.
I think it would be wise to download any digital files immediately if you need them as there is no guarantee they will be permanently available. I do.