From my application I'm sending email but email client (for example Mozilla Thunderbird) blocks the images. I use image urls from my website.
Is any way to prevent the image blocking by email clients ?
No. How do you expect to force a 3rd party application to download data it doesn't want to download? All you could do is make your email unreadable without downloading the images, which will increase the likelihood of both being treated as spam and of being deleted unread.