Drag/drop pictures from Google to Mp3Tag


I often search pictures in Google Pictures and I drag and drop them onto the the album art rectangle on the lower left side of the Mp3Tag window (XP-Firefox3.6-Mp3Tag2.46a).
I notice a strange behaviour. Often it works fine. But sometimes it does not work at all, dropping is not allowed. Then I have to right-click, "copy image" in Google, right-click, "Paste cover" in Mp3Tag. Very tedious but it always works.
Very small pictures (below 200x200 pixels) can not be dragged/dropped at all as it seams but medium sized pictures also do not work here and there.
I searched but did not find the right answer. What have I missed?


I think that not all files in the internet are jpg or png. GIF, BMP, tif and so on are available as well and I think that these formats do not work as album art.

The problem also occurs with jpegs.

It seems, that especially preview pictures doesn't work - but I can't tell you why. Maybe they have some "special" link that prevent the drag & drop-feature? Or maybe it depends on the number of pixels/size/resolution?