This tag indicates that an image is sampled from Pawoo and thus not the original size.
Pawoo has thumbnails of images that display from the timeline, and they are distinguishable by the presence of [code]/small/[/code] in the URL. An example from this toot:
- Original: https://img.pawoo.net/media_attachments/files/000/587/250/original/941f9c5672f1c22f.png
- Sample: https://img.pawoo.net/media_attachments/files/000/587/250/small/941f9c5672f1c22f.png
Pawoo samples are very easily distinguishable from their original counterparts due to their diminutive size. Always make sure you use either the bookmarklet or upload page on the original toot to make sure you don't upload them.
It is Danbooru policy to either replace samples or delete them. See Image Sample for more information. See Help:Pawoo for how to upload images from Pawoo correctly.