In the past, the by tag was used for the Creative Commons attribution license. Check the image source(s). If the image is licensed under the Creative Commons attribution license, cc-by should be used instead, see https://e621.net/forum_topics/36564. If the image is not licensed under cc-by, remove this tag.

*IMPORTANT* by is commonly mistagged onto an image if the uploader attempts to attribute the author by adding "by AUTHOR" into the tag field. Care should be taken to ensure images that are not licensed under cc-by are not mistakenly tagged as such.