onepixel.png warning

Hi,

Thank you for the plugin and your effort. I have been using it for some time.
I just noticed the below line in the plugin page—actually, there are two lines with the same error.

Any idea if there is some rights error or for what onepixel.png is used in the plugin?

Warning: copy(https://zzz.com/wp-content/plugins/send-pdf-for-contact-form-7/images/onepixel.png): failed to open stream: HTTP request failed! HTTP/1.0 403 Forbidden in /home/xyz/public_html/zzz.com/wp-content/plugins/send-pdf-for-contact-form-7/classes/send-pdf.php on line 606