[Unofficial – use at your own risk]
Here’s how I do a rollout of a Sparkle website with a large number of images (one of my clients has 4,656 images as of today, for instance):
Using Transmit (FTP):
Create an “images-new” folder on the website.
Upload contents of the exported “images” folder to this new folder.
While these are uploading:
a. Delete the older site icons on the live site (files with a date/timestamp suffix)
b. Queue up the upload all the website files except for the “images” folder (in Transmit, this upload will not begin until all the images have been uploaded [step 2]).
Once (2) and (3) are complete:
a. Rename the previous live “images” folder to “images_prev1” or similar, or delete it (takes longer).
b. Rename the newly-populated “images-new” folder to “images" (to make it live).
You may ask why I wouldn’t use Sparkle’s own FTP client to handle a site like this. I could, but I like to minimize the downtime of the website, which only happens briefly as I rename the images folders. I use Transmit’s fly-out activity progress bar(s) to watch for when the mother lode upload of images is complete.