Didn't you tried to add not 1 picture/sound in one time?
This bug happened when I had a bunch of sound to add in a project, I clicked “Upload sound from file” and selected a lot of sounds, clicked Open. I expected that Scratch will load all this file but after a while my Google Chrome wrote me: “Shockwave Flash has crashed” . Other pages that used Flash player crashed too(in flash player i saw dead puzzle piece.
I'm using Windows 7. My browser is Google chrome(note that my google chrome cant check for updates so I don't know what version it is)