According to Section 1202 of the U.S. Copyright Act:

No person shall, without the authority of the copyright owner or the law—

 

(1) intentionally remove or alter any copyright management information,

 

(2) distribute or import for distribution copyright management information knowing that the copyright management information has been removed or altered without authority of the copyright owner or the law

I don't know of any rulings that point to watermarks specifically but as per subsection C, "copyright management information" is defined to include the following, which indicate watermarks are valid:

...
2) The name of, and other identifying information about, the author of a work.
...
7) Identifying numbers or symbols referring to such information or links to such information

You may elect to recover either actual damages or statutory damages:

Except as otherwise provided in this title, a person committing a violation of section 1201 or 1202 is liable for either

 

(A) the actual damages and any additional profits of the violator

 

(B) At any time before final judgment is entered, a complaining party may elect to recover an award of statutory damages for each violation of section 1202 in the sum of not less than $2,500 or more than $25,000.

According to Section 1202 of the U.S. Copyright Act:

No person shall, without the authority of the copyright owner or the law—

(1) intentionally remove or alter any copyright management information,

(2) distribute or import for distribution copyright management information knowing that the copyright management information has been removed or altered without authority of the copyright owner or the law

I don't know of any rulings that point to watermarks specifically but as per subsection C, "copyright management information" is defined to include the following, which indicate watermarks are valid:

...
2) The name of, and other identifying information about, the author of a work.
...
7) Identifying numbers or symbols referring to such information or links to such information

You may elect to recover either actual damages or statutory damages:

Except as otherwise provided in this title, a person committing a violation of section 1201 or 1202 is liable for either

(A) the actual damages and any additional profits of the violator

(B) At any time before final judgment is entered, a complaining party may elect to recover an award of statutory damages for each violation of section 1202 in the sum of not less than $2,500 or more than $25,000.

According to Section 1202 of the U.S. Copyright Act:

No person shall, without the authority of the copyright owner or the law—

(1) intentionally remove or alter any copyright management information,

(2) distribute or import for distribution copyright management information knowing that the copyright management information has been removed or altered without authority of the copyright owner or the law

I don't know of any rulings that point to watermarks specifically but any information that provides details of ownership should suffice to fall under "copyright management information".

You may elect to recover either actual damages or statutory damages:

Except as otherwise provided in this title, a person committing a violation of section 1201 or 1202 is liable for either

(A) the actual damages and any additional profits of the violator

(B) At any time before final judgment is entered, a complaining party may elect to recover an award of statutory damages for each violation of section 1202 in the sum of not less than $2,500 or more than $25,000.

According to Section 1202 of the U.S. Copyright Act:

No person shall, without the authority of the copyright owner or the law—

(1) intentionally remove or alter any copyright management information,

(2) distribute or import for distribution copyright management information knowing that the copyright management information has been removed or altered without authority of the copyright owner or the law

I don't know of any rulings that point to watermarks specifically but as per subsection C, "copyright management information" is defined to include the following, which indicate watermarks are valid:

...
2) The name of, and other identifying information about, the author of a work.
...
7) Identifying numbers or symbols referring to such information or links to such information

You may elect to recover either actual damages or statutory damages:

Except as otherwise provided in this title, a person committing a violation of section 1201 or 1202 is liable for either

(A) the actual damages and any additional profits of the violator

(B) At any time before final judgment is entered, a complaining party may elect to recover an award of statutory damages for each violation of section 1202 in the sum of not less than $2,500 or more than $25,000.