I have heard some reports that:
Entering the shown text ("reCAPTCHA V1 IS SHUTDOWN") will let you pass.
Entering any text will let you pass.
But if that's not true, then you'll have to wait until the site is updated.
Tricking the site itself should be impossible for a properly programmed website. Most bypass methods instead rely on convincing reCAPTCHA's ...
Turn off SSL.
I had the same issue after setting the SSL toggle on (it's in "edit appearance"). Turning off SSL fixed the issue and the captcha works now. I emailed Tumblr to let them know, hopefully it's a quick fix.
I don't believe and haven't found this (length of time till maturity) listed. It's most likely intentionally ambiguous to keep those that are suspicious guessing. Things you can try
Verifying your account by cell number
Interacting with Facebook profiles (friends)
Avoiding proxies (sacrifice of privacy but some proxies allow many spammers to be welcomed)
You can create your own simple CAPTCHA by inserting a multiple choice
question like this:
How much is three plus seven?
( ) Don't know ( ) 9 ( ) 10 ( ) 11
Use the "Go to page based on answer" option to jump back to the page
where the CAPTCHA is, or to the next page in the event the humanoid
filling the form gets it ...
If you think that you are being blocked because your ISP share IPs among a lot of users (shared public IP address):
ask your ISP if they could assign you
to a different group of users
a dedicated IP address
change of ISP.
From "Unusual traffic from your computer network"
I shouldn't be getting blocked
Google Search ...