First you must have an upload form in your HTML, notice that the file input field in the form below is profile_pic

<form action="/uploadme" method="post" enctype="multipart/form-data" name="upload-photo">
 <input name="profile_pic" type="file" />
 <input type="submit" value="submit"/>
</form>

In Controller, create an instance of DooGdImage, along with the upload/source path and the path to save your resized pictures:

 Doo::loadHelper('DooGdImage');
 //upload/source path, and output saved path
 $gd = new DooGdImage('/var/www/uploaded/', '/var/www/resized_pic/');

Call uploadImage() to save the uploaded file with a new name. The example below save the picture with the date as file name, img_20100104203245.jpg

$uploadImg = $gd->uploadImage('profile_pic', 'img_' .date('Ymdhis'));

Before your resize the picture, you can set the quality, generated image type and file name suffix (optional)

 $gd->generatedQuality = 85;
 $uploadImage->generatedType="jpg";

 //This thumbnail is 46x46 pixels, resize adaptively (perfect 46x46 crop from center)
 //Pic name is img_201001011200_46x46.jpg
 $gd->thumbSuffix = '_46x46';
 $gd->adaptiveResize($uploadImg,46,46);

You can use createThumb/createSquare to resize the pictures too.

 //Resize propotionally (so will not be perfect 75x75 depends on the image ratio, no cropping done)
 //Pic name is img_201001011200_75x75.jpg
 $gd->thumbSuffix = '_75x75';
 $gd->createThumb($uploadImg, 75, 75);

Some updates*

You can validate if the uploaded images meet your requirements by using checkImageType(), checkImageSize() and checkImageExtension()

• checkImageType() – check if image mime type is in the allowed list. Default: JPEGs, GIFs and PNGs
• checkImageExtension() – check if image file extension is in the allowed list. Default: jpg, jpeg, gif, png
• checkImageSize() – check if image file size does not exceed the max file size allowed (KB)

if($gd->checkImageExtension('pfile')){
    $gd->uploadImage('pfile');
}

//or provide your own allowed list
$ext = array('jpg','jpeg','gif','png','bmp','tiff');
if($gd->checkImageExtension('pfile'), $ext){
    $gd->uploadImage('pfile');
}

Related links:

Picture example of images generated by adaptiveResize()
Questions on using DooGdImage.