Noticeable but small differences

While using the image search feature before uploading any of my posts (as to avoid double posting) I've come across quite a few images with noticeable but small differences. As an example:

post #210687 I have an image saved on my computer which looks exactly like this except the colors look more solid and not quite as washed (it may be hard to notice since I can't link the shot to compare it to). I'm not trying to hate on the OP but I'm curious as to what Danbooru's position is on something like this (didn't see anything in the help section on this subject).

As another example, post #278818 doesn't look quite as sharp as the same image I have. Even the image search picks up on it saying it has 82% similarity (the only difference possibly being sharper colors and lines, even though it's the same content).

At first I thought the easy solution would be just to post the images I have as child posts but figured it would be better to get another person's opinion on the matter rather than risk image deletion. My apologies if this matter has been touched on many times.

Well... I'm going to tell you now that you'd best be sure that the image is GOOD first. Both of the images you linked are quite old, and danbooru's standards have risen since they were posted. Porn is judged on it's artistic merit and game CGs are almost completely ignored now. Look at howto:upload (and the pages it links to) for general advice.

That said, if you have a picture that is higher quality than an existing image that is worth the upload, proper parenting would be the best course of action.