It’s possible to make the images larger by giving larger values to some size properties of ReallySimpleCaptcha class. However, CAPTCHAs naturally trouble some users even if you make them larger. I’d recommend using Akismet instead of CAPTCHA.
See Spam Filtering with Akismet
I’ve posted this response also to Contact Form 7 responsive but Really Simple Captcha not
I eventually managed to fix this by increasing the size of the image in my theme’s style.css by 110% for both height and width for the captcha image. It is looking good now for all platforms. Anything greater than 110% is risky. However this meant changing the CSS site-wide, as in ‘.row .col img’ h & w 110%.
Hopefully there is a more reliable way to fix this in CSS.
Thank you Mr Miyoshi. Contact Form 7 and Really Simple Captcha are the best.
