Changing Image Size Already Uploaded Images

[motty07]

Hi

When I insert an image into a post, say 730 px by 547 px, it automatically inserts width and height parameters.

<img class="alignleft size-quite-large wp-image-1552" title="Chrysanthemum" src="http://localhost/wordpress/wp-content/uploads/2012/02/Chrysanthemum-730x547.jpg" alt="" width="730" height="547" />

Now what happens in a year's time if I decided to change my site layout to one where the content width is say 500 pixels.

Will have to go into every post and re-upload a resized image?

I realise that I can add a max-width parameter to the css. This will display the image at the reduced width but will also skew the images - unacceptable. It's also just loading the larger image and just scaling it down - inefficient.

[update - can add height inherit property to css: e.g. max-width: 300px; height:inherit; - but still using original size image - no skewing but still inefficient]

I've also seen plugins such as Simple Image Size/Regenerate Thumbnails that regenerate image sizes. But they don't change the image dimensions of the code.

Surely there must be a workaround? I'm sure when people change themes they don't have to go into each post and manually edit the code/reupload images?

Thanks in advance.