It did not work. You clicked again and again, but in vain.
You only kept seeing the tiny spinning ball changing colors (red, blue, green, orange and yellow), the image could not be uploaded.
After a long times, probably you may manage to upload the photo into your blog post.
It's a very nerve-racking and time-wasting experience..
So what is wrong?
According to Google/Blogger, it could be popup blocker, plugins or you need to clear your cache.
As for me, it was one of your FireFox Addons called SEO Global For Google Search addon.
I just have it disabled and then restart my FireFox and I have no problem uploading Blogger photos.
If your problem is not caused by this Firefox add-on , then you can try signing out from Blogger.
Then clear cache and cookies. And restart your PC.