Just when I thought I had solved this ... it has suddenly reappeared.
on Monday 12th I added this to my config.php..
define( 'WPCF7_CAPTCHA_TMP_DIR', 'mycaptcha/' );
The dir gets populated with the imags and php files
However today I get the notification of
File Name: /home/sites/mywp/public_html/wp-content/uploads/wpcf7_captcha/134249777.php
Dec 14, 14:51
I think there is still an issue whereby Ccf7 is reverting back to the default uploads dir.