I looked at this, thinking it would be easy to do with a couple of AppleScript files. It turned, we needed to patch GarageSale to cope with tightened macOS sandbox restrictions.
So, once you have downloaded GS 9.8 Beta 6 (GarageSale 9.8 Alpha 6 Released), you can give this AppleScript a go.
It lets you pick a folder, and every JPEG image at the top level of this folder will get turned into a listing in GarageSale with that image.
Every subfolder in the folder you picked will get turned into a listing, too, having all images it contains added.
Confusingly, GarageSale might ask you to pick that folder once again, that work around sandbox reading restrictions.
Paste this into Script Editor:
use AppleScript version "2.4" -- Yosemite (10.10) or later
use scripting additions
tell application "Finder"
set theFolder to (choose folder)
set theFiles to (name of every file in theFolder)
try
set theFolders to (name of every folder in theFolder)
on error
display alert "No folders were found in the selected folder"
error number -128
end try
end tell
set theFolderPath to theFolder as string
repeat with theFile in theFiles
if the theFile ends with ".jpeg" or theFile ends with ".jpg" then
set fileAlias to (theFolderPath & theFile) as alias
createListing(theFile as string, {fileAlias})
end if
end repeat
repeat with aFolder in theFolders
set folderAlias to (theFolderPath & aFolder) as alias
set imageFileAliases to {}
tell application "Finder"
set imageFiles to (name of every file in folderAlias)
repeat with imageFileName in imageFiles
set imageAlias to ((folderAlias as string) & imageFileName) as alias
set imageFileAliases to imageFileAliases & imageAlias
end repeat
end tell
createListing(aFolder as string, imageFileAliases)
end repeat
on createListing(listingName, images)
tell application "GarageSale"
set theListing to make ebay listing
tell theListing
set title to listingName
repeat with theImageFile in images
if (the theImageFile as string) ends with ".jpeg" or (the theImageFile as string) ends with ".jpg" then
set imagePath to POSIX path of theImageFile
set theImage to make listing image file imagePath
end if
end repeat
end tell
end tell
end createListing
Let me know how it works for you.