For the hard-cooked egg aioli: Place the eggs in a single layer in a straight-sided sauce pan, and cover completely with water. Bring to a boil, and then remove from the heat and cover tightly with a lid, 15 minutes.
Immediately shock the eggs in an ice bath. When the eggs are cool enough to handle, gently peel off the shells and finely chop.
Stir together the mayonnaise, dill, horseradish, mustard and capers until combined. Fold in the eggs, and season with salt and pepper. Cover and refrigerate at least 30 minutes to allow the flavors to meld.
For assembly: Slice the bread into 1/2-inch slices, and then cut each slice lengthwise into 3 or 4 pieces to create 35 to 40 crostini.
Top each crostini with a slice of salmon and a dollop of the aioli, and garnish with dill fronds.