[Plugin: Contact Form 7] Manual fields inside the form.

I need my user to mark pictures from my blog that are dynamically inserted in the contact form.
When user submits the contact form to send me the message the information about selected pictures would be sent to my mail.

What I figured out till now is to pass value from fields my PHP code creates to the fields created by Contact Form 7. But I suppose there should be less perverted way of doing that ??

The best solution I see is the possibility to combine form fields that I create with PHP and those that are created by Contact Form 7 plugin, being sent together within one form.

Example of what I need.

Name: (TEXT FIELD)
Email: (TEXT FIELD)
IMG (CHECKBOX), IMG2 (CHECKBOX), IMG3 (CHECKBOX), IMG4 (CHECKBOX)
Message: (TEXTFIELD)
Submit button.

Thanks for help.