We have a web based accounting software, and severly need to connect to scanners and operate them via our programs. What can be used? PHP, Javascript,... to do that? ??????

None of the above...

Scanner cannot be controlled by scripting language like PHP or JavaScript. Scanners rely on drivers in most cases written for a specific operating system which then allow graphical or other input program to interface with those drivers.

In order to have a "custom" applications be able to talk to your scanners, your best bet is to hire some one to write a custom interface that will work with your accounting software and a TWAIN device. TWAIN (Technology Without An Interesting Name) is a standard for getting input from image scanners: an image capture API for Microsoft Windows and Apple Macintosh operating systems.

It's doubtfully that you will fine the solution you seek on this forum.

I imagine it should be possible to develop a Java applet or an ActiveX component that hooks into TWAIN libraries. This would require the client computer to accept, download, and successfully install your custom-developed object.

If you can choose between Java and ActiveX, I recommend Java because it can be platform independent. ActiveX is IE and Windows Only.

You might try the software development forums here (not web dev) to see if you can find a Java applet guru. Try the Java forum at http://daniweb.com/techtalkforums/forum9.html

Good luck. If you work out a solution, be sure to post a follow up for those that come after you.