Questions continue to mount about Pinterest's uneasy relationship with copyright law, with one attorney (and avid Pinterest user) saying the company needs to upgrade its Digital Millenium Copyright Act policies or risk being shut down.

Connie Mableson, an attorney in Phoenix, offers a point-by-point breakdown of where Pinterest's DMCA policy could get the increasingly popular social network into trouble. The problems range from simple clerical errors, like forgetting to update its registered designated agent as required by the act, to more serious problems, like failing to include "repeat infringer" language in the policy as required by federal digital copyright law.

"A few simple changes will make this DMCA lawyer much more comfortable knowing her pins will not suddenly disappear one day when Pinterest is out of business due to paying other lawyers exorbitant amounts of money to defend it against claims of copyright infringement," Mableson wrote.

We've asked Pinterest to respond to Mableson's blog post and will update when they get back to us.

Mableson's post was published on the same weekend that Flickr confirmed its site upgrade included code to prevent Pinterest users from pinning copyrighted images. The move is significant, as Flickr is the third most popular site for Pinterest content.

"Flickr has implemented the tag and it appears on all non-public/non-safe pages, as well as when a member has disabled sharing of their Flickr content," a Flickr representative told VentureBeat Friday. "This means only content that is 'safe,' 'public' and has the sharing button enabled can be pinned to Pinterest."

To date, Pinterest has been relatively quiet on its copyright policies, and copyright attorneys have been divided on what liability users have when they share content on the site. While the DMCA allows publishers to avoid liability for content posted by users, the flaws pointed out by Mableson could nullify those protections.