Replace the question mark with a fitting image.
A fitting image would be:
i.e. a picture of ice hockey legend, Wayne Gretzky.
Why? First identify the people in the images. These are all...
...ice hockey players who have played in the NHL:
Left side: Eric Lindros, Paul Kariya, Mario Lemieux, and Jaromír Jágr.
Right side: Brett Hull, Pat LaFontaine, Pavel Bure, and Glenn Anderson.
Now note the image depicting a jersey with a red square...
We need to find the jersey numbers worn by these players. The numbers most famously associated with them all (and indeed retired by their clubs in most cases) are:
88 | 9 | 66 | 68
16 | 16 | 10 | 9
(This information can be found from Wikipedia, although Jágr's 68 doesn't feature in this list as I don't believe it's officially been retired yet...)
Now note the topmost part of the puzzle.
This list of digits represents concatenated odd numbers (greater than 1).
We need to focus on the numbers from the two pools of player faces that are odd numbers. In each case there is only one in each: Kariya's 9 and Anderson's 9.
(EDIT: The OP points out in comments that this was actually intended as a rebus for 'odd-one-out' - hence the only odd number outside the box being the '1'. Either way, I still managed to arrive at the intended answer, as the reason one player was the odd-one-out in each case was because they had an odd-numbered jersey!)
Put these together as per the two side-by-side red boxes and you get:
99, the number famously worn by Wayne Gretzky, whose shirt number 99 has been retired across the whole of the NHL in recognition of his achievements on the ice (hence a slippery puzzle in the title!).