Hellströem

>>151140120
It's Unix Time; How many seconds have passed since 1970 started. 4chan used to add three extra numbers, which were always assumed to be miliseconds, but some time in the last two years (forgot when) this was bumped-up to 6 extra digits, to thwart the glitch where two images would be uploaded at that exact time and both would get one's thumbnail.

Also, it's a lot of images.