Any way to upload image to an S3 bucket through ExtendScript?

Yes you would call a Powershell script which calls cURL. Here is a sample (uploading to ftp but the idea is the same.)

#Sample Powershell script to upload files to ftp using curl

#Notes: File paths and directories should be edited to suit. Script will fail around 1400 files in a folder, keep it under that.
#If a different ftp account is needed, add a new item to the array with login:pass
#--ssl -k used for ftps account

#edit these variables
$curlpath = "~\curl\bin\curl.exe"
$MasterDir = "~\Pictures\"
$ftpDir = "ftps://ftp.sample.com/"
#subdirectories, logins, file types - (local folder, remote folder, file extension, file type)
$DirArray = ("PDF", "pdf/", ".pdf", "PDF"), ("Small JPEG", "JPEG/1000px/", ".jpg", "JPEG"),`
("Large JPEG", "JPEG/1600px/", ".jpg", "JPEG")
$ArrayCounter = 0
#add item to array for account with different password
$pass = "user:password"

#spreadsheet
$ftp = $ftpDir+"Excel/"
$filelist = "sample.xlsx"
cd ~\Desktop\
Start-Process -FilePath $curlpath -ArgumentList "-T $filelist $ftp -u $pass --ssl -k"

#repeat until end of DirArray
while ($ArrayCounter -lt $DirArray.length)
{
#get parameters for next directory
$Dir = $MasterDir+$DirArray[$ArrayCounter][0]
$RemoteDir = $DirArray[$ArrayCounter][1]
$searchext = $DirArray[$ArrayCounter][2]
$filetype = $DirArray[$ArrayCounter][3]
#if needed for different account
#$pass = $DirArray[$ArrayCounter][4]

#get file listing filtered by $searchext and convert to globbed input for curl
$filelist = dir $Dir ("*"+$searchext)
$filelist = $filelist -replace($searchext,',') -replace ($filetype,"")
$filelist = "{"+$filelist+"}"
$filelist = $filelist -replace(',}',('}'+$searchext)) -replace (' ','')

#launch curl if list is not empty, upload from local directory
if ($filelist -ne "{}")
{
#specify ftp server directory
$ftp = $ftpDir+$RemoteDir
#change local directory
cd $Dir
Start-Process -FilePath $curlpath -ArgumentList "-T $filelist $ftp -u $pass --ssl -k"
}
$ArrayCounter = $ArrayCounter+1
}