Things you need to consider..
Type of site: Informational, Education or Entertainment?
Type of visitor: Many users just upload photos directly from their cameras (these images are 1000+ in widths)
- many users do not know how to decrease photo size
- many users do not know how to decrease size of an image
- many users do not even own an image editor
- many users do not want to bother with the above
Now, that you know a little about the end-user you need to consider what is important to you..
1)__ Do you want to make it easy for your members?
2)__ Do you want to keep costs down? (resources)