10 karma · joined July 29, 2015
I'm not too sure about what defines the "distinctive" signature of recaptcha, but I expect timing of when packets of certain sizes were sent (e.g. loading 9 images in quick succession will generate larger packets, and then you often get the incremental couple images with human-length delays between them).
Relatedly, Tor recommends all users use HTTPS[3], as otherwise the connection from the exit node to the target site is vulnerable to MITM. Given that there are malicious exit nodes[4], seems like a good idea. But, as the article brings to light, that still doesn't make any guarantees of safety.
[1] https://en.wikipedia.org/wiki/Room_641A [2] e.g. http://www.infoworld.com/article/2925839/net-neutrality/code... [3] https://www.torproject.org/docs/faq.html.en#CanExitNodesEave... [4] e.g. http://www.cs.kau.se/philwint/spoiled_onions/ but plenty of other sources