This approach could work, but it becomes less efficient as the number of gaps increase in both frequency and size. More importantly, it is also much trickier to insert a new element or change the order of the elements. I realize that neither insertion nor reordering were specified requirements in the OP, but I was trying to generalize the solution and anticipate future needs^*. A linked list would handle those requirements easily.

^*I've never been part of a project that hasn't had some degree of feature creep, and this one seems likely. "Oh, good - we can delete pictures. Hey, can we add them, too?"