The signature will be automaticly Copyright protected without Registration that is true!

I Repeat Ilegall it is to pretend that you created an Image that another Made. Also the Copyright of Digital Images have not been addapted to the Law it goes under Application's Law( Digital Applications ) not to be confused with Paintings and materialistic copyright.

so as for using fragments of Provided free Images for a Collage on a Texturing would be  a Legal Usage! as Long as your Eula does not pretend that all the contains are made by your self giving credit to the originall creator or if not known giving credit to a Image collection of uhnknown Providers , as Digital Imaging mostly do not have a signature of the originall creator.

It also depends on where you come from as each Cautry handles Copyright in a different way , In swiss it is waay more flexible then In the US witch is rather the case to prevent artists to be creative.

We Here can for example Buy a PS3 change the HD and will not Loose the guarantee. we are allowed to save any digital Product on the Internet , witch is not allowed in the States. It is even Allowed to create a Digital Copy of your Bought DVD's or Music cd's and store them as Backup or for usage on a server.

So to say each has to Consult the regional law about Copyright.

If a Product is offered for Free and is not further Protected it is commen sence that it is a gift . You can cut , in this case an image appart and Make the collage as you wish.