The method I use is to resize the pic (save a new copy) I set mine at the longest side 700 pixals - but I reckon about 850 would get on, save the image using JPG compression so that it is no larger than (I think) 117Kb - but preferably below 100.
Do your reply and select manage attachments and brows for the pic - then upload and then submit and Bingo - it should appear!
Geoff Chandler. UK/England/Surrey
NIKON D90 / D80. Nikon 16 - 85 VR, Tamron 28-200,
Sigma 70-300APO, Tokina 100 AT-X Pro D.
SB600 flash. Panasonic DMC-TZ25