I have a 600x600 pixel pic which is 240 KB. If you upload a 240KB pic which is 600x600 pixel you will get a warning. I have optimized the pic that is 600x600 pixel from 240 KB to something smaller size, 185 KB, but still 600x600 pixel by doing:
Would optimizing the pic in Photoshop result in disqualification?
Photoshop -> File -> Save For the Web -> Optimized