I have been selecting the images and corresponding text boxes in excel first, then hitting ctrl+c to copy. Then I hit ctrl+v to paste into Paint, ctrl+x to cut out of Paint, and ctrl+alt+v to paste into a new image into paint.NET.
I just tried to use different methods of copy-paste to no avail.
pdnnoob, I think you are right, it corresponds to where in the Excel document the image is. I tried copying an image that is several inches down in the document and it doesn't even show up on the canvas at all, I'm thinking it is several inches down in paint.NET as well.
I tried pasting into a new layer of an existing image and I don't think that will work either. The little preview it gives you when it asks whether you want to expand the canvas or resize the picture showed the image offset as well, so it seems like it just comes out of Excel like that. Not sure why. Anybody have any other ideas? I'm about to resign to just pasting and cutting out of Paint first from now on.