-- save in Script Editor as an Application, then
-- drag image files onto the Application's icon
on open some_items
    repeat with this_item in some_items
        try
            rescale_and_save(this_item)
        end try
    end repeat
end open

to rescale_and_save(this_item)
    tell application "Image Events"
        launch
        set the target_width to 120
        -- open the image file
        set this_image to open this_item
        set typ to file type of this_image
        copy dimensions of this_image to {current_width, current_height}
        if current_width is greater than current_height then
            scale this_image to size target_width
        else
            -- figure out new height
            -- y2 = (y1 * x2) / x1
            set the new_height to (current_height * target_width) / current_width
            scale this_image to size new_height
        end if

        tell application "Finder" to set new_item to (container of this_item as string) & "scaled." & (name of this_item)
        save this_image in new_item as typ
    end tell
end rescale_and_save

property openTypes : {"PDF", "com.adobe.pdf", "BMP", "com.microsoft.bmp", "JPEG", "JPEG2", "jpg", "public.jpeg", ¬
    "PICT", "com.apple.pict", "PNG", "public.png", "PSD", "com.adobe.photoshop-image", "TIFF", "public.tiff"}

--Get the artwork file
set theFiles to choose file with prompt "Choose art file(s)" of type openTypes with multiple selections allowed without invisibles
runConversion(theFiles)

on open someFiles
    runConversion(someFiles)
end open

on runConversion(theItems)
    set saveFolder to choose folder with prompt "Save resized pictures where?" without multiple selections allowed and invisibles
    tell application "Image Events"
        launch
        set newHeight to 600
        set newWidth to 0
        if (count items of theItems) is greater than 0 then
            repeat with anItem in theItems
                set imageFile to (open anItem)
                set theSize to dimensions of imageFile
                set width to item 1 of theSize
                set height to item 2 of theSize
                set ratio to (width / height)
                set newWidth to (ratio * newHeight) as integer
                if newHeight > newWidth then
                    scale imageFile to size newHeight
                else
                    scale imageFile to size newWidth
                end if
                save imageFile as JPEG in saveFolder
                close imageFile
            end repeat
        else
            display dialog "Nothing to convert."
        end if
    end tell
end runConversion

global theImage

-- Prompt the user to select a file
set theImage to choose file with prompt "Please select an image file:" without invisibles
-- Prompt the user to enter the width of the picture
set theResult to display dialog "Saisissez la largeur de l'image." default answer "640"
set theAnswer to text returned of theResult

-- Retrieve the resize percentage amount
set theNewWidth to theAnswer as integer

-- Determine a path in which to save the resized image
tell application "Finder"
    set theImageName to name of theImage
    set theImageFolder to (folder of theImage) as string
end tell
set theResizedImagePath to theImageFolder & "Resized-" & theImageName as string

-- Open the image, resize it, and save it as a new file
tell application "Image Events"
    launch
    set theImage to open theImage

    -- This is the tricky part: you need to keep the ratio of the original picture
    copy dimensions of theImage to {currentWidth, currentHeight}
    set ratio to theNewWidth / currentWidth

    tell theImage
        scale by factor ratio to size theNewWidth
        save in theResizedImagePath
        close
    end tell
end tell

set this_file to choose file

try
    tell application "Image Events"
        launch
        set this_image to open this_file
        scale this_image to size 318
        rotate this_image to angle 45
        pad this_image to dimensions {800, 600}
        save this_image with icon
        close this_image
    end tell
on error error_message
    display dialog error_message
end try