Execute an application on Mac OS X when a particular type of USB device is connected?

You can use launchd. Try man launchd and man launchd.plist.

It seems that launchd can work with USB events, even though this feature is poorly documented. I found it on: man xpc_set_event_stream_handler

Here's an example. If you put the following into: ~/Library/LaunchAgents/com.example.plist, your program should start when a USB device is connected.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC -//Apple Computer//DTD PLIST 1.0//EN http://www.apple.com/DTDs/PropertyList-1.0.dtd >
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>com.example.program</string>
    <key>ProgramArguments</key>
    <array>
    <string>/path/to/program</string>
    </array>
    <key>LaunchEvents</key>
    <dict>
            <key>com.apple.iokit.matching</key>
            <dict>
                    <key>com.apple.device-attach</key>
                    <dict>
                            <key>idProduct</key>
                            <integer>1234</integer>
                            <key>idVendor</key>
                            <integer>1337</integer>
                            <key>IOProviderClass</key>
                            <string>IOUSBDevice</string>
                            <key>IOMatchLaunchStream</key>
                            <true/>
                    </dict>
            </dict>
    </dict>
</dict>
</plist>

Depending on the type of device you might able to set an application to open automatically via the iPhoto/Image Capture preferences. That will work only for a limited class of devices, for an application already present on the computer and will require changing the preferences on the computer manually.

In general, there's no way to automatically run arbitrary applications on CD/DVD/USB insert because it's a security problem.

Julien Pilet's answer worked for me. However, to get it to not constantly relaunch the app when the device is still connected when closing the app, I had to:

• call xpc_set_event_stream_handler() in my app delegate applicationDidFinishLaunching:

    xpc_set_event_stream_handler("com.apple.iokit.matching", NULL, ^(xpc_object_t event) {     
        // Every event has the key XPC_EVENT_KEY_NAME set to a string that
        // is the name you gave the event in your launchd.plist.
        const char *name = xpc_dictionary_get_string(event, XPC_EVENT_KEY_NAME);

        // IOKit events have the IORegistryEntryNumber as a payload.
        uint64_t id = xpc_dictionary_get_uint64(event, "IOMatchLaunchServiceID");
        // Reconstruct the node you were interested in here using the IOKit
        // APIs.
        NSLog(@"Received event: %s: %llu",name,id);
    });

• add KeepAlive/false key/value pair to the plist
• add IOMatchLaunchStream/true key/value pair to the com.apple.device-attach dict in the plist. This is in addition to the IOMatchStream key already there. Not sure why that has to be there, I found a reference to it here: http://asciiwwdc.com/2013/sessions/702

Also don't forget to register the plist with the system using

launchctl load <path to your plist>

Note that this seems to work, but I never get the NSLog message from the xpc stream handler.