Is the fetch function not getting the best possible image?

Twice now I’ve uploaded a picture to this site using the Fetch function, only for it not to be the highest quality and for someone else to re-upload it and merge with a higher resolution one.
 
Is the Fetch function not really that useful in this way?

@Toastypk  
Is it from DeviantArt? Because if so, it’s because DeviantArt is constantly changing things specifically to fuck over sites like derpi, almost more than it tries to fuck over its own users.

@The Smiling Pony  
Yes both times were from DA.  
Though I do the Fetch function all the time there anyway.

@The Smiling Pony  
Sometimes they do so multiple times a week.
 
@Toastypk  
DeviantArt usually has a section on the image called ‘IMAGE DETAILS’ which includes the (supposedly) uploaded image size. That is usually the maximum size that is available. So if you get a smaller version from DA than the ‘IMAGE DETAILS’ information, then you don’t have the best image you can get. Sometimes the artist enables the DA ‘Download’ button which theoretically SHOULD give you the maximum size available, but that also changes over time.
 
There have always been ways to hand code a download request from DA that tends to get the best possible image size, but from time to time they ‘make a new one for you’ and it ends up with artifacts.
 
And, invariably, just as you figure out the new string to get the best image size downloaded, DA will change it. I mean, the last time I looked it the URL literally had the image’s size in the URL, but while just editing that sometimes works, sometimes it doesn’t.
 
For myself, I use the Fetch function, because that gets the image on the site. And if the resulting image in the upload is smaller than what I was expecting, I try a few ways of opening the file directly on DA to get a better size if possible. If not, then I look to see if the artist has other places they upload images where a better version might be available.
 
So, the Fetch function is quick and easy and tends to give the best result that is possible via automated means (as of that moment), but at any time, night or day, DA might ‘fix’ things so it doesn’t result in the best size image. Despite that, it’s still a good way to populate things like artist tag and the source url, and then you can find the ‘better image’ by hand before committing to the upload.

I’ve also found it can happen with Tumblr. Recently, it fetched a 1280-wide image when I could see via inspector that an 1800-wide was available (which I subsequently uploaded to have merged).