Does the Silent Image spell require the caster to actually have visual contact with the area they want to place the effect on?

Question

Does the silent image spell require the caster to actually have visual contact with the area they want to place the effect on?

Or, is the 60-foot radius all that matters, even if it is behind a wall?

To be even more specific,

1. What about if it is a 15-foot area in a location in range that you have seen before but is now out of sight?
2. What about when on your turn you have visual contact with an enemy in a certain area, then move behind some cover and then you wish to place the illusion area around the enemy and within the 60-foot range?

I am asking because I have seen other illusion spells' descriptions that specify that you must see where you place your spell. Silent image doesn't specify whether the sight component is or isn't required.

All spells require an unobstructed path from caster to target.
Spells that say "that you can see" require the caster to be able to see the target, in addition to an unobstructed path. If the spell does not say "that you can see" then there is no requirement for the caster to see the target.

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Background behind the question

You always need a clear path to target a creature with a spell.
A creature behind total cover cannot be targeted.
But, you don't necessarily need to be able to see them, just that the travel path is clear such as a thick fog (unless the spell specifies that you need you see the target).
The example of a glass window is brought up: no you cannot target something through glass, even if you can see them; the glass provides total cover.
There are spells that create exceptions to the above: such as Sacred Flame, which specifies that it gains no benefit from cover for the saving throw(such as from half, or 3/4 cover), but also that total cover does not protect them.
So for example, Sacred Flame CAN target someone through a clear window, but not through a thick fog."
A spell does not need line of sight, unless it says so.
All spells require an unobstructed path from caster to target.
Spells that say "that you can see" require the caster to be able to see the target, in addition to an unobstructed path.
If the spell does not say "that you can see" then there is no requirement for the caster to see the target. They still need the unobstructed path.
In this episode of the Official D&D Podcast, Jeremy Crawford specifically calls out a closed window (at about 34 mins) - and says it blocks casting.

Answer 1

No

There are no secret rules

Under the general rules for spellcasting the target (any point on any face of the 15-foot cube) must be within range (60 feet) and there must be a clear path to it. The rules for Silent Image add nothing to this so you are not required to be able to see the target or, for that matter, any part of the cube.

For your specific examples: 1. OK, if there is a clear path, 2. Not OK as there is no clear path.

There are no restrictions other than range on moving the image. Not even the clear path requirement although some DMs may balk at that.

For those who wonder how the spellcaster can create a realistic image without seeing it? Easy, magic.

Answer 2

The spell does not state that you must be able to see a target spot, so technically no; however, a dungeon master may interpret that your need to be able to see the area for Silent Image is implied by the text of the spell.

You can use your action to cause the image to move to any spot within range. As the image changes location, you can alter its appearance so that its movements appear natural for the image. For example, if you create an image of a creature and move it, you can alter the image so that it appears to be walking.

Because you are controlling the image through the intuition of your caster for up to 10 minutes it is necessary to see the area, leastwise you cannot control the meshing of the image properly. It may be that the concentration on the spell requires active visual engagement in your phantasmal creation.

The reality is that when we try to line up a bolt with a nut on two sides of a plane we cannot see we often need to line up after feeling with our hands. This is good evidence that our blind spatial sense is inaccurate. At a longer unseen range, going by intuition alone without our sight we may be very far off. Thinking about this kind of experience in our own lives helps makes it obvious that to successfully use this spell we would need to see the space it will occupy. Especially when creating a more complicated image. This may not hold true for the image of a flying dragon because if it is in the open sky it may not need meshing into the background or real. If you create the image of a flying dragon it may be enough that there is a flying dragon regardless of how accurately you place the image in the sky or have it fly in a specific fashion or trajectory.