These images are hosted in a Content Delivery Network (CDN) that is part of your paid Tweak account. The Tweak CSS you use in Ecwid will get the images needed for your Ecwid shop from your Tweak CDN.
If you do not want to use the Tweak CDN, you can host the images yourself, and then cancel your subscription and continue using a free Tweak account with no CDN. Note. Beta account users will need to subscribe before the end of June 2014, or host their images themselves.
To host the images yourself, you must get a zip copy of your CDN contents, extract all the images and host them yourself on your own server.
See this article for the details of the CDN zip, how to get it and how to use it.
You can request a CDN zip from your profile page with an active Beta, Subscription or PAYG plan, and also while your account is suspended for 30 days after your plan has ended. If your account has expired, a CDN zip will have been automatically created for you and will be available from your profile page. If you have any difficulties getting a CDN zip for an expired account, contact firstname.lastname@example.org
Tweak - can I use the free plan or should I subscribe?