control Paste (Ctrl+P) Image size in RichTextBox

I can do an context menu with a item of Paste, and in it I can control what image type is (width, height, resolution, format...), then for example I can msgbox when the user try to paste (using contextmenu) a too big image.

but if the user uses Control+P the paste occurs whitout my code.

then

1.- ¿how can I run some code with Paste and optionally cancel the paste?

2.- ¿how can I reduce the format (colors)?
i.e. the cb.image has Format32, how to reduce to Format8?

btw seems to be that clipboard.paste allways have Format32.