Mmm, I retract some of my approval for the new photo uploading arrangements. It works perfectly for the "ladies" camera that I keep in the car and use for closer access at exhibitions, but not for the "proper" camera that I used to take some pictures of the West Coast Main Line that runs a couple of hundred yards away from the venue.
I presume that size is the issue, though the error message just calls it a 'problem'. I could resize them, I suppose - what is the actual limit, though? I could use the existing Imgur link, as I have elsewhere, but that's https and doesn't work, either.
It took me a while to realise that I had used a different camera outside.
For reference, about 1M works and about 4M doesn't (for me).