Since you mention it, I don't see any need for there to be an "edit mode" or a placeholder in the first place.
Yes, not for screenshots or posters.
There are already controls on the images. The only one that behaves differently is "load from file." It replaces the existing image, and should be called "replace from file."
It was an unpleasant surprise when I discovered that and also that the replaced image wasn't even moved to the Recycle Bin.
Add a "delete" button, then everything—including some control over the ordering of images (by inserting and deleting)—can be done without having to go into edit mode.
I agree--and for posters, why the need for the buttons below the image (the left arrow, right arrow, and the plus). The left and right arrows are only for people who haven't discovered left- and right-clicking on the image does the same thing (and for those people there should be tooltips that say "Left-click on image" and "Right-click on image"). The Plus button, in its current state, is also redundant, but as you say below, it could be converted.
What would be useful would be "Move Left" and "Move Right" buttons for changing the order of posters. For single movements, that would be faster than opening up a separate interface to change the order by drag-and-dropping.
Regardless, there's no need for buttons on that row that has the "1 of 12" data. What could go in the extra space there instead is a custom item for notes about each poster like "Fan created vs. official" "Web site of origin," "Rating," "Look for a bigger size," "Watermark in annoying place," "Adult content," "Country poster is used in" "Production or behind-the-scenes photo," "True poster vs. DVD cover" (for when a DVD cover is all that's available or that you prefer it over the true poster) etc. If one custom item wasn't enough, then more could added to additional rows, but you could fit at least one on that "1 of 12" row.
One other thing that would be good is if there were a mode to make screenshots work like posters, where you just right-click on them to advance to the next one. If you have 50 screenshots and want to quickly flip through all of them, double-clicking on each is cumbersome.
I do like that you now have the option to "Show random poster" like you can for People photos. When I'm looking on the web for new movies to watch, they often have foreign language titles its hard to remember, so I have to rely on the poster thumbnail, which means I have to visually memorize all the variants, even the posters I don't care for. Thus PVD now serves the function of flash cards.
Add another one for "add from file"—to add another image after the selected one.
Yes, it doesn't make sense to have to right-click through a dozen posters to get the Plus button to show up only beneath the last one (where its faster to just right-click again to add a poster anyway).
The only thing that would make this better is the ability to drag & drop images to change their order.
Yep, every time I use Listal.com and drag the posters around so easily, I wish I could do this in PVD. The only thing I'd like more is a 'Load/Paste from Clipboard' button like eXtreme Movie Manager has.