Adding Image Verification to a Submit Form (not the contact us form)

[kewldude_3001]

For some reason, I always get junk from bots on my submit form but not on my contact us form. If someone knows why that would be nice.

 

So to prevent bots from using the form, I want to add this Image Verification.

 

I got as far as adding it to my form, but the thing is my form emails me the form contents so it uses gdform.php and i didnt know where to add the rest of the code I need to ensure that the image verification was entered correctly in order for it to submit the form.