Update image alt tags using Sitecore PowerShell Extensions.

Update-AltTags.ps1

$rootPath = "/content/Company/DotCom/usa/home"
$file = "$($SitecoreDataFolder)\temp\alt-tags.csv"
$records = Import-Csv -Path $file
$totalCount = $records.Count
$currentCount = 0
$activity = "Updating alt tags"
foreach($record in $records) {
    $currentCount += 1
    $percentComplete = $currentCount / $totalCount * 100
    $itemPath = $rootPath + ($record.Url -replace "www.Company.com","")
    Write-Progress -Activity $activity -Status "Checking if item exists" -PercentComplete $percentComplete -CurrentOperation $itemPath
    if(-not (Test-Path -Path "master:$($itemPath)")) { continue }
    $page = Get-Item -Path "master:$($itemPath)"
    $mediaID = $page.PSFields.HeadlineImage.MediaID
    Write-Progress -Activity $activity -Status "Checking if image exists" -PercentComplete $percentComplete -CurrentOperation $mediaID
    $image = Get-Item -Path "master:" -ID $mediaID
    if(!$image) { continue }
    if([string]::IsNullOrEmpty($image.Alt) -and ![string]::IsNullOrEmpty($record."Alt Tag")) {
        Write-Host "Updating $($image.ItemPath)"
        Write-Progress -Activity $activity -Status "Updating alt text for image" -PercentComplete $percentComplete -CurrentOperation $image.Alt
        $image.Alt = $record."Alt Tag"
    }
}

Write-Progress -Completed -Activity "Completed processing update"