Since Dynamic Web TWAIN version 6.1, we simplified the installation process for using the plug-in edition in Chrome, Safari and Opera.
After installation of Dynamic Web TWAIN Plug-in, you will find a file DynamicWebTWAINPlugIn.exe along with DynamicWebTwain.xpi in the installation folder.
To allow your end users to use the scanning SDK in Safari/Opera, you can put a download link of DynamicWebTWAINPlugIn.exe on your web page, so that your user can download the EXE file and install it on the client machine. After that, the user can access your application and scan images via Safari/Opera browser.
You may check how this can be implemented on Dynamsoft Online Demo.