Does that mean, that I can use that image(and other such images found on wallpaper hosting websites) without worrying about its license and attribution?

No!

Someone owns the rights to that image. If you are not the holder of the rights to that image or if the owner has not granted you a license to use the image then you are not allowed to use the image. If you decide to use the image anyway and the owner of the image decides to pursue legal action against you the civil penalties can be quite severe. In addition to actual damages (basically the amount you would have had to pay to properly license the way you used the image plus any amount you profited from your use of the image) you can also be liable for punitive damages that can go into the hundreds of thousands of dollars per violation.

If you used digital technology to gain access to the image, in the United States you can also be criminally liable under the Digital Millennium Copyright Act of 1998 (DMCA). Many other countries have similar criminal statutes, particularly those that have agreed to the Berne Convention for the Protection of Literary and Artistic Works.

If you wish to argue that the image is "public domain" or licensed under a Creative Commons or similar type of license, then the burden of proof is on you to show that. You should not use an image unless and until you can show that either:

• The image is in the public domain
• The image is covered under a Creative Commons License or other such license that grants generic users certain royalty free usage of an image
• The owner of the rights to the image (i.e. the copyright holder or their assignee) has granted you a license to use the image in the way you wish