darkazma said:

Here's the case:

93.2 KB (95,480 bytes) v.s. 93.2 KB (95,526 bytes)

Then I used SSIM to compare them , the result is 0.9999561 , not equal to 1

I checked my deleted post , SSIM is 1

So if the image size is bigger than the post on e621 and their SSIM is not equal to 1, (and same image type, ex:jpg)

Can I reupload the post?

Or recommend other algorithms or approaches?

For a few bytes? No.