What size does an image have to be in order to upload it?

[Gorgett Core]

Second Life doesn't give a specific value of what size (ex: picas, pixels, etc.) it just tells me that the picture can't be bigger than 2048*2048. 

[Rolig Loon]

No, in fact it cannot have pixel dimensions any larger than 1024 x 1024.  It's actually more restrictive than that.  All pixel dimensions must be powers of 2 (32, 64, 128, 256, 512, or 1024).  If you try to upload images with dimensions that do not meet those specifications, they will be automatically resized downward.

See http://wiki.secondlife.com/wiki/Limits#All_Viewers