Hi wertyu (I've just noticed how you arrived at your login name!)
There is no doubt that this is blatant infringement of your copyright, if they have gone to the trouble of editing out the logos.
You are right that, should this ever get to court (hopefully not) then you would be faced with proving these were your images and therefore that you are the copyright owner, but that is relatively easy, assuming you still have the original digital files which should be dated with the creation date plus any modification date (eg when the watermark was added. This data should appear in two separate parts of the metadata of the file: the basic file data and the EXIF data, although it has to be said both are relatively trivial to spoof. Thus if you have a file with a date which precedes the date of the infringing video, it will then be for the other party to explain the anomaly. However I suspect they won't try and claim that they originated these images - that's pretty hard to prove if you aren't the originator - and instead they will claim some nonsense about either being unaware these images were copyright, or claiming they obtained them legally from another source. Neither defence would stand up in court. Furthermore, since it seems highly probable (although you may not be able to prove it) that they were responsible for removing your logos, then it is likely they have also breached section 296ZA of the Copyright Designs and Patents Act 1988:
296ZA Circumvention of technological measures
(1) This section applies where—
- (a) effective technological measures have been applied to a copyright work other than a computer program; and
(b) a person (B) does anything which circumvents those measures knowing, or with reasonable grounds to know, that he is pursuing that objective.
(2) This section does not apply where a person, for the purposes of research into cryptography, does anything which circumvents effective technological measures unless in so doing, or in issuing information derived from that research, he affects prejudicially the rights of the copyright owner.
(3) The following persons have the same rights against B as a copyright owner has in respect of an infringement of copyright—
- (a) a person—
the work to which effective technological measures have been applied; and
- (i) issuing to the public copies of, or
(ii) communicating to the public,
(b) the copyright owner or his exclusive licensee, if he is not the person specified in paragraph (a).
(4) The rights conferred by subsection (3) are concurrent, and sections 101(3) and 102(1) to (4) apply, in proceedings under this section, in relation to persons with concurrent rights as they apply, in proceedings mentioned in those provisions, in relation to a copyright owner and exclusive licensee with concurrent rights.
(5) The following provisions apply in relation to proceedings under this section as in relation to proceedings under Part 1 (copyright)—
- (a) sections 104 to 106 of this Act (presumptions as to certain matters relating to copyright); and
(b) section 72 of the Senior Courts Act 1981, section 15 of the Law Reform (Miscellaneous Provisions) (Scotland) Act 1985 and section 94A of the Judicature (Northern Ireland) Act 1978 (withdrawal of privilege against self-incrimination in certain proceedings relating to intellectual property).
(6) Subsections (1) to (4) and (5)(b) and any other provision of this Act as it has effect for the purposes of those subsections apply, with any necessary adaptations, to rights in performances, publication right and database right.
(7) The provisions of regulation 22 (presumptions relevant to database right) of the Copyright and Rights in Databases Regulations 1997 (SI 1997/3032) apply in proceedings brought by virtue of this section in relation to database right.
Although there is no caselaw on this specific topic, it is widely believed that a digital watermark applied to an image would fall within the definition of technical measure provided by the Act:
“technological measures” are any technology, device or component which is designed, in the normal course of its operation, to protect a copyright work other than a computer program.
The most likely course of action for you lies in using Youtube's takedown system to get the video removed, and at the same time writing to the person responsible for the video, and outlining your complaint and what you want him to do by way of remedy. This could just be to stop any further publication of the video, or perhaps some sort of financial settlement in recompense for his infringement.