I came here looking for the same answer.
I think I've figured it out. Your photo needs to be a maximum of 150 x 150, and less than 50 KiB. You can use a site like picnik to resize your photo (type in your specific size specs), save, then upload from your computer. HTH!
Heather (PAI-1 4G/4G) mama to:
Nicolas Edison (6/2004) 36 weeks, PE, HELLP, and placental abruption
Ella Amelia (3/2007) 37 weeks, lovenox, PE-free
Oliver Lyon (1/2011) 37 weeks, lovenox, PE-free
Milo Mason (2/2014) 39 weeks PE-free