Overriding the Concrete5 Image block to not print out width & height attributes

controller.php

<?php 
	defined('C5_EXECUTE') or die("Access Denied.");	
/*
 * How to make overrides/extend controllers in Concrete v5.6+
 * 1. Create a new file & put your opening & closing PHP tags
 * 2. Add line 2 above (execute or die!)
 * 3. Go to (root)/concrete/blocks/block-you-want-to-override/file-you-want-to-override.php
 * 4. You'll see something like 'class somethingBlah extends somethingElse_blah'. Copy that with the opening & closing brackets
 * 5. Now go to (root)/concrete/core/controllers/blocks/file-you-want-to-change.php
 * 6. Open said file and look at the functions inside of it. Copy from 'function... { stuff... }' --being sure to include the closing bracket
 * 7. Change what you want in that specific function (add/edit/delete stuff)
 * 8. Save the new file you just made to (root)/blocks/block-you-want-to-override/file-you-want-to-change.php
 * 9. Log into Concrete5 & disable all things cache--especially the overrides cache, cause that's what we're changing
 * 10. Refresh the page and watch magic happen!

 * Below is an override of the default Image block in C5.6.0.2 where I've removed 
 * the width, height, & border attributes from printing in the DOM ( {$sizeStr} and border=\"0\" )
 * This essentially enables your images to shrink porportionally when you do responsive design
 * Place this file in (root)/blocks/image. (You'll probably have to create the image folder if you haven't already)
*/
	class ImageBlockController extends Concrete5_Controller_Block_Image {

		function getContentAndGenerate($align = false, $style = false, $id = null) {
			$c = Page::getCurrentPage();
			$bID = $this->bID;
			
			$f = $this->getFileObject();
			$fullPath = $f->getPath();
			$relPath = $f->getRelativePath();			
			$size = @getimagesize($fullPath);
			if (empty($size)) {
				echo t( 'Image Not Found. ');
			    return '';
			}	
			
			if ($this->maxWidth == $size[0] && $this->maxHeight == $size[1]) {
				$sizeStr = $size[3];
			} else if (!$this->forceImageToMatchDimensions && ($this->maxWidth > 0 || $this->maxHeight > 0)) { 
				$mw = $this->maxWidth > 0 ? $this->maxWidth : $size[0];
				$mh = $this->maxHeight > 0 ? $this->maxHeight : $size[1];
				$ih = Loader::helper('image');
				$thumb = $ih->getThumbnail($f, $mw, $mh);
				$sizeStr = ' width="' . $thumb->width . '" height="' . $thumb->height . '"';
				$relPath = $thumb->src;
			} else {
				$sizeStr = $size[3];
			}
			
			$img = "<img class=\"ccm-image-block\" alt=\"{$this->altText}\" src=\"{$relPath}\" ";
			$img .= ($align) ? "align=\"{$align}\" " : '';
			
			$img .= ($style) ? "style=\"{$style}\" " : '';
			if($this->fOnstateID != 0) {
				$fos = $this->getFileOnstateObject();
				$fullPathOnstate = $f->getPath();
				$sizehover = @getimagesize($fullPathOnstate);

				if ($this->maxWidth == $sizehover[0] && $this->maxHeight == $sizehover[1]) {
					$relPathHover = $fos->getRelativePath();
				} else if (!$this->forceImageToMatchDimensions && ($this->maxWidth > 0 || $this->maxHeight > 0)) {
					$thumbHover = $ih->getThumbnail($fos, $mw, $mh);				
					$relPathHover = $thumbHover->src;
				} else {
					$relPathHover = $fos->getRelativePath();
				}

				$img .= " onmouseover=\"this.src = '{$relPathHover}'\" ";
				$img .= " onmouseout=\"this.src = '{$relPath}'\" ";
			}
			
			$img .= ($id) ? "id=\"{$id}\" " : "";
			$img .= "/>";
			
			$linkURL = $this->getLinkURL();
			if (!empty($linkURL)) {
				$img = "<a href=\"{$linkURL}\">" . $img ."</a>";
			}
			return $img;
		}
	}
?>

As a side note, if all you want are responsive images that scale, you can actually leave the default controller alone if you add img { max-width: 100%; height: auto; }.