9999 People reached

Is this question about Facebook? Instagram? Snapchat? Pinterest? Tumblr? Something else?

It's highly likely that this is a somewhat viral image being shared but you need to be considerably more specific before anyone can answer you intelligently.

We're talking about Facebook here.

Then it's likely what I said; you're watching a viral image being shared in, more or less, real time. Facebook refreshes its large, complex, and powerful database as soon as it can, every few seconds or so. It is also refreshed when you hop from FB page to FB page (or app, or group, etc.). The refreshing is what shows the numerical uptick.