I'm not trying to make an appeal or an argument or anything, just want to know what I did wrong so I can avoid doing it in the future

this was the post by the way: https://e621.net/posts/3387799

and I'm not entirely sure what I did wrong; I followed the formatting guidelines and got proper resolution, tagged everything I could, put in all the proper links for the sources, and even posted it first but it still got deleted for being a 'duplicate/inferior post' in favor of one that was posted after the fact.

Can someone tell me what I messed up? I'd rather avoid getting any more posts deleted for that reason.

The reason is written in the red box on the post page. Someone uploaded a bigger version of the same picture and the inferior was deleted.

Edit: it looks like you uploaded a JPG. it compresses images and artifacts are visible, due to that. PNG file are loss less and have no artifacts.

dubsthefox said:
The reason is written in the red box on the post page. Someone uploaded a bigger version of the same picture and the inferior was deleted.

Edit: it looks like you uploaded a JPG. it compresses images and artifacts are visible, due to that. PNG file are loss less and have no artifacts.

okay how do I fix that when posting?

gameguy82 said:
okay how do I fix that when posting?

The Sites and Sources wiki page contains a guide that will help you find the best possible version of any given image.

gameguy82 said:
okay how do I fix that when posting?

Basically, find image you like then do what gattonero said to learn which sites are the best and how to acquire files from them. Cross-reference it with the available websites the artists posts on to be able to find the best pubic version of a post.

Likely sources
Deviantart = Good if the download button is a available
FurAffinity = Good if the artist bypassed the 1280p compression, otherwise bad
Twitter = Usually bad converting most things to jpg, also has a hard limit on 4096p so will downscale anything larger. Low resolution or low color pallet images can sneak by getting file converted though.
Inkbunny = Good, just make sure you don't grab a 920p width example scale image from the source
Newgrounds = Good for a 1 image post, bad for multiple images after the first, 2nd+ are just thumbnails
Mega.nz = Good
Dropbox = Good

there are other sources, but these are the more common ones from my personal experience.

gameguy82 said:
okay how do I fix that when posting?

Get the original file directly from the artist if possible. It saves you all the hassle from multiple galleries and their limitations.

https://e621.net/deleted_posts?user_id=2124428
This one? Too many deleted my post... High quality