I know nothing of the 'yahoo to the new site "flickr"', but as know one has replied.....
This is what I would do...First you need to find out if you have enough pixels. To do this I would save one of the photos and insert it in a Word Doc & format it. If you can 'pull' your photo out from one of the corner anchor points to reasonable size then you have your answer. The exact answer for resizing someone else may help.
If as soon as you start to 'pull' your photo out and it looses its sharpness etc. Then the problem I would presume is "flickr", which has reduced it to send to you.
Worth a go until someone else replies.