More zero article bafflement
Solution 1:
When you say "the picture" you are using the word the to indicate that it's a specific picture, not just "a picture."
However, when you say "picture number 24" you don't need to use the to signify that it is a specific picture. The fact that you have named the picture provides the specificity.
Technically "picture number 24" could be the title of the picture, in which case it would be a proper noun and capitalized. Even as a common noun, though, the same principle of specificity applies.