Hello,
I’m new here, and I’ve never used Piwik. I would like to use Piwik with several blogs but I don’t want that everyone could know that I use Piwik on my blogs.
So, my question is : If someone check the source code, Could he know that there is piwik installed on my blog ?
(Sorry for my English 
)
Thank you for your help guys !
Yes Piwik will be shown in the source code (eg. the tracker file is called piwik.js)
You can however hide the fact that the same piwik is tracking several websites. for this see this FAQ: How to - Analytics Platform - Matomo
You can also use different tracking methods than js e.g. analyze directly web server’s logs or using tracking api, this way no footprint in the source code presented by browser - http://piwik.org/faq/new-to-piwik/#faq_63
cheers