Hi,
Typically that error is preceded by some sort of PHP error or warning but can also happen if some whitespace (spaces or newlines) are output before the image.
It could potentially be another plugin generating the output or an issue with this plugin version you are using.
From Settings >> Securimage-WP, can you check the box labeled “Debug Image Errors”, save the settings and then click the “View Image Directly” link and see the result?
If you are still getting the error, copy & paste the HTML source code of the page to pastebin.com and post the link here. If there was any whitespace output, it should appear in the page source.
Also, if possible, try disabling all other plugins and see if the image appears, then re-enable them one at a time until the error appears again and let me know if it was a specific plugin causing the problem so I can release a fix.
You can also email me directly using https://www.phpcaptcha.org/contact/ and I can take a look at your site and see if I can find out what is happening.
Thanks.
