the word 'public' is given a very restrictive meaning. I give you a few examples:

If a sculpture is available in the park, the sculpture can be reproduced without any infringement.

If a piece of artwork is available in a particular platform it is not readily accessible to be counted as 'public'. There must be some action taken to access the platform and access the drawing. In that context the intellectual property still belongs to the author. What is readily available in google images does not amount to public space because google is a search engine, all work are actually a link to the site. Unless google maintains a separate collection of pictures that the authors willingly choose to place in that location/server for public's access. That would be more likely to be interpret as 'public'.

If a web is accessible to the public but upon access to the site, there is a reminder to the visitor that the artwork is to be respected and cannot be reproduced without the author's permission, that reminder itself would be an assertion of the author's right and the law would respect that.

The basic idea about public access is the author in so choosing the place to display without any caveat on his/her rights invites a legal assumption that the right is waived.