I've been considering uploading some of strega's (https://aryion.com/g4/user/Strega) newer work, and I'm having trouble telling whether to use feral or anthro for some of their characters.
For instance, https://aryion.com/g4/view/876589 is clearly bestiality, and Uragh is clearly feral. However, https://aryion.com/g4/view/880177, with the same characters, they both appear anthro to me, despite strega labeling them both as feral.
In https://aryion.com/g4/view/886526, which I uploaded as https://e621.net/posts/4011196, I initially thought of both characters as anthro. However, with the context of the other images, I'm not as sure.
Any advice on telling the difference?

Judging by the images you have shown, they all appear to be feral characters. However, if you are planning to upload these artworks, I’d suggest you use the semi-anthro tag along with feral, considering one of the characters has a somewhat anthro-like anatomy.

All of those images you linked should be tagged as feral. The body shape and proportions are both feral. For it to be anthro either the legs would be a lot longer or the body shape would be very different.