In Windows 7, (using MP3tag 2.57, but also in previous version) I can no longer drag & drop pictures into the picture field. my cursor now changes into an "illegal" sign (you know, like a road sign banning you from driving into the road from that direction. I now have to save the image to HD and load it using RMB -> Add cover).
Yes, I also get that behaviour when I d&d an image from an internet browser.
Which program do you use to drag from? Firefox? Internet Explorer?
I think that these programs create an html-link (at least that is what I get when I drag an image into the explorer). HTML-Links are no valid picture types.
It works fine if you d&d a real image file from the file explorer into the picture box.
Edit for append:
I checked around a little and finally got hold of a Win 7 machine: on most internet pages it is still possible to d&d pictures - yet, the Google picture search page does not allow it. This page creates a link (and that is an invalid data type).
Just a test: if you try to d&d from this forum page e.g. the mp3tag logo then it will most certainly work.
Please note that only PNG and JPG are valid cover formats. GIFs and BMP are not (I think)
You can't d&d a picture from the Google picture search overview page, that's right.
But if you click on a picture you will see a "copy" in the middle of the screen (with some rows of preview pictures above and under the usable one). You can also see some kind of progress bar directly under the new copied picture itself. At least for very big pictures.
If you d&d THIS single picture in the middle of the page, it still works fine.
Thank you for confirmation and more insight.
In short I would say: no bug, only source-dependent.