Third party Captcha not responsive

This is really a limitation of the CAPTCHA provider -- the image provided is that wide and I don't think that chopping it off or shrinking it would be ideal.
 
You should avoid reCaptcha. It has been cracked years ago, so Google made it more complex trying to beat spam bots. Result is these days bots have easier time reading it than humans.

Use Q&A captcha instead. It is responsive.
 
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