According to the law, you can use an older work of art by a long-deceased creator. For example, when publishing a photo of a painting, the photographer who took the picture of the painting has the copyright and must be credited as the image source. Authors also have intellectual rights to their works, which means that you may not change anything in it, nor present it in a context that could be perceived as offensive to the artistic personality of the author. The most important thing to remember is to always credit the image source.