Set Locked = true for the image node and the diagram will select the node behind it. If you don't wish to lock it, you could change the selection from the NodeClicked event handler if e.Node is the image node.

I hope that helps,
Stoyan

When NodeClicked is raised, e.MousePosition gives you the mouse position in diagram coordinates. You can subtract the origin of e.Node.Bounds from it to find the mouse position relative to the node. Then you should be able to find the position of the image pixel from the node-relative point depending on the ImageAlign value you are using. E.g. if ImageAlign is Stretch, the image pixel should be (image.Width * nodePoint.X / node.Bounds.Width, image.Height * nodePoint.Y / node.Bounds.Height).

I hope that helps,
Stoyan

Call GetNodesAt to get a list of all nodes at the specified position. They are sorted in reverse Z order, so the transparent node should be at index 0, and the one below it at index 1. If your application allows stacking many transparent nodes on top of each other, I suppose you could loop over the returned collection until finding a non-transparent node to select.

I hope that helps,
Stoyan