Content on the web is copyrighted in the same way as print and other formats are, even if there is no copyright symbol (©) or copyright notice. Linking directly to the web page containing the content you wish to use is almost always permissible, although you should look for a statement on "Terms of Use" or "Legal Notices" on the website in question to ensure that linking is not prohibited. You should always include the full details of the author, the copyright owner, and the source of the materials by the link. This will avoid any suggestion that the website being linked to consists of your own material or that the website containing the link is somehow affiliated with the website being linked to.
Whether or not you request permission to link to a website, if you have reason to believe that the website contains content posted without the permission of the copyright owner, you should avoid linking to it.