def do_image_upload(theFile)
    # You should reall set these two in a config.
    maxFilesize = 10485760
    fileDir = "public/files"

    fileName = Time.now.to_i.to_s + '-' + rand(36**8).to_s(36) + File.extname(theFile[:filename])
    filePath = File.join(fileDir, fileName)

    tempFile = theFile[:tempfile]

    upload = {
        :fileSize => tempFile.size,
        :originalFileName => theFile[:filename],
        :fileType => theFile[:type],
        :fileName => fileName,
        :filePath => filePath
    }

    if upload[:fileType] != 'image/png' && upload[:fileType] != 'image/jpeg' && upload[:fileType] != 'image/gif'
        return {'fileError' => 'FileType not allowed.'}
    end
    if upload[:fileSize] > maxFileSize
        return {'fileError' => 'FileSize too large.'}
    end

    if !File.directory?(fileDir)
        return {'fileError' => 'Destination ' + directory + ' does not exist.'}
    end
        
    if !File.writable?(fileDir)
        return {'fileError' => 'Cannot write to ' + directory + '.'}
    end

    File.open(filePath, "wb") { |f| f.write(tempFile.read) }

    return upload
end

Checks to make sure the file is a valid image file, checks max file size, and directory write permissions, requires 'fileutils' gem.

Image Uploading in Ruby

image, file, ruby

Ruby