Policy on dead source links?

The source link on post #7377744 goes to a deleted twitter account, but the tumblr account linked on the artist's wiki page has a post with the same image that's still available.

I was initially going to just replace the dead link with the alive one but after reading the howto:tag wiki page when prompted to, I thought I'd ask first since neither the howto:tag wiki page nor the howto:tag checklist wiki page have any guidance on what to do with dead source links, and the former mentions that you should ask for help on the forums.

If the post on the Tumblr account has a matching MD5 (you try uploading it and it redirects you to the existing Danbooru post; should not be confused with pixel-perfect duplicate or otherwise) and is definitely a first-party source, you can replace the post's source yourself. Otherwise, it should be left alone, and you can upload the Tumblr post as the parent if it's superior or not at all if it's inferior.

Dead sources should never be replaced with alive ones except when a first-party source has a matching MD5.

You can refer to https://danbooru.donmai.us/wiki_pages/bad_id for guidance.

Bad ID covers what to do in this situation, which is to say, there's two options:

1) you just tag the appropriate Bad ID tag and leave it like that for the rest of time;
2) if, somehow, the artist has the art available on another account and (and this is crucial) the filesize and MD5 of the new sources's image is identical to that of the artist's old source, then you can change the source field and avoid adding the Bad ID tags.

The latter happens way less frequently these days because social media platforms mess with the filesize and MD5 of uploaded images more and more, so it's possibly unlikely that the Tumblr source you've linked matches the Twitter one in both.

WRS said:

If the post on the Tumblr account has a matching MD5 [...]

As far as I can tell, they do not have a matching MD5 hash.

WRS said:

[...] you can upload the Tumblr post as the parent if it's superior or not at all if it's inferior.

What if they're the same? I'm using this image comparison tool on the image from tumblr and the downloaded image from post #7377744 and it shows that there is no difference between the two of them. They also have the same width, height, and DPI.

The wiki page on pixel perfect duplicates mentions that a pixel-perfect duplicate post which was uploaded after the original or has no source is considered inferior but what about when the source link on the original post is dead, and the new post has a first-party source?

not404 said:

As far as I can tell, they do not have a matching MD5 hash.

What if they're the same? I'm using this image comparison tool on the image from tumblr and the downloaded image from post #7377744 and it shows that there is no difference between the two of them. They also have the same width, height, and DPI.

The wiki page on pixel perfect duplicates mentions that a pixel-perfect duplicate post which was uploaded after the original or has no source is considered inferior but what about when the source link on the original post is dead, and the new post has a first-party source?

If the posts are pixel-perfect duplicates but aren’t the same file, you can ask for an image replacement in topic #16765.

By the way, to make a tag plural while keeping the link valid, you can just type “s” immediately after the brackets. Just mentioning that because I noticed you typed the whole thing inside the brackets and it can be a bit inconvenient to do that sometimes.