The reason that the flag was declined was not because the images were okay or acceptable, but because regular users of the Stack Overflow community are empowered to handle a lot of basic, janitorial moderation tasks.
Even as a user with less than 500 reputation, you can suggest an edit by removing the images. Not only would you gain 2 reputation points once your edit is accepted, but it also frees up the moderators to stay focused on handling the exceptional cases that the community is unable to resolve.
This takes some getting used to, as Stack Exchange sites are not like traditional forums. You have the power. [Insert animated GIF of HE-MAN here].
See the Stack Overflow Privileges page for a list of the various reputation thresholds and the tasks that you can perform at each level. Good luck!