You know who you are! If you entered a photograph that is too large.

[HappyCynic]

3. One method

I always scale down my images prior to uploading them. I process the image as normal and export it at its normal size. Then I resize the exported image using Irfanview (with the jpeg quality set to 100%) and check the size. If it's over 675k, I lower the jpeg quality by a single percentage point and repeat until it's under the limit. (I can almost always export at 100% without hitting the limit.)
I upload the smaller image to the photo site and use that for posting to DU.

Caveat: I don't need to post full size photos, as DU is pretty much the only place I post my photos. As a result, I only upload the smaller images to Flickr. So, doing this is less of a hassle for me than for many others, who want/need to have full size images on their photo sharing site. Maintaining a separate photo album with the smaller images would be an option but would require more work and would also push you closer to any limits (like number of photos or total memory limits) so it's not a solution for everyone.