[GD help when saving file]

Late to reply to this but thought it may serve as useful for anyone hitting on this as I did from Google.

 

A quick and easy way to force the browser to allow you to save as a particular filename and/or extension is to pass the filename and extension into the URL (or form action depending on how you are generating the image)

 

eg as a form post

<form name="myform" action="picgenerator.php?name=thepic.jpg" method="post">...

 

or as just a URL (in the querystring)

http://www.mywebsite.com/picgenerator.php?name=thepic.jpg

 

Now, right-clicking on the image and choosing "Save as" (or equivalent, depending on which browser you are using) will save the file as a jpeg defaulting to the name thepic.jpg

 

Works for all browsers (as far as I know)