I apologize for the trouble you experienced trying to get dynamic number insertion to work with images. Admittedly, our previous method for image substitution was confusing. We’ve updated our docs and simplified our procedure: http://www.callrail.com/docs/web-integration/dynamic-number-insertion/images/
Anyone that is having issues is welcome to call us directly at 888-907-4718 and we will work with you to troubleshoot the issue.
Disclosure: I’m a CallRail co-founder