Hello churu,
If you simply want to return the image to the original state, keep a copy of the original in memory and re-apply to the picturebox as needed.
For instance, you could declare the original as a global variable.
Dim Original As Image
Load the image as such.
Original = Image.FromFile("filepath")
When you need to revert...
Picturebox.Image = Original.Clone
This only allows you revert back to the original. If you want more control over the undo, you will need to devise a scheme to keep copies of the image as you edit. Maybe store the images in an ImageList for retrieval.
Another method is to keep track of the edits and re-apply all but the last when undo is selected.
Both of these methods are certainly more complex, but infinitely more flexiable.