I love illusions, including Silent Image, but unfortunately I don't think it's always handled correctly. I'd like to clarify the RAW interpretation of this spell for this purpose.
Here is the text of the spell:
You create the image of an object, a creature, or some other visible phenomenon that is no larger than a 15-foot cube. [...]
Physical interaction with the image reveals it to be an illusion, because things can pass through it. [...] If a creature discerns the illusion for what it is, the creature can see through the image.
When Silent Image is cast, and this image has been revealed to be illusory, do they still see the image as opaque? Unlike spells like Minor Illusion, this spell does not specify that creatures can see this illusion as if it was transparent.
It does say: If a creature discerns the illusion for what it is, the creature can see through the image. I don't think this is supposed to be taken literally, otherwise it would have said the illusion becomes faint to the creature as it does for Minor Illusion. Also, "to see through something" is an idiomatic expression meaning "to understand the true nature of something."