Keep div height while the image is loading

Question

I have a square image within .img-container. Sometimes it takes a few seconds for an image to load and the .img-container collapses and only takes the full height when the image loads. However, I would like it to keep the full height (as if the image is there) while the image is loading.

I would've easily done this by setting a min-height on img-container class, however it's a fluid grid and the image is responsive (notice bootstrap's img-responsive helper class) which makes it hard to set the min-height to an appropriate value for different screen sizes (although achievable with media queries as a last resort). Solving this by putting a placeholding image sounds like an overkill (especially performance wise on mobile). Also, not sure what would load first then, the placeholder image or the actual image.

<div class="col-xs-12 col-sm-6 col-md-4 col-lg-4">
    <div class="card">
      <span class="img-container thumbnail clearfix">
        <img alt class="pull-left img-responsive" src="http://...">
      </span>
      <div class="caption">
        <a href="http://.." class="card-title lead">
          Some text
        </a>
      </div>
    </div>
  </div>

Answer 1

EDIT DUE TO COMMENT

If you do not specify a source at all (not even a dummy, temporary one), the browser will not even try to "guess" the image's height, and so it collapses. If you know the ratio of the image (it's obviously 1:1 in case of a square picture), you can use the following trick to preoccupy the space, and scale the image along with the div.

Set the following CSS:

.test-div-inner {
    padding-bottom:100%;
    background:#EEE;
    height:0;
    position:relative;
}
.test-image {
    width:100%;
    height:100%;
    display:block;
    position:absolute;
}

Then you can use the following HTML:

<div class="test-div-inner">
    <img class="test-image" src="https://www.ilikewallpaper.net/ipad-air-wallpapers/download/4556/Andromeda-Galaxy-ipad-4-wallpaper-ilikewallpaper_com_1024.jpg">
</div>

Here is the working example: http://jsfiddle.net/pQ5zh/3/

Note that the fiddle contains another div element, this is only required if you would like to give it all a padding or border, since the padding-bottom calculates the padding in pixels based on the width of the div INCLUDING THOSE PARAMETERS, which is NOT the effect we want to achieve (the image would be a little taller than it should be).

For non-square images:

If you would like to change the ratio of the picture, just change the padding-bottom of the container div accordingly. For example, if you would like to place an image with a ratio of 2:1, change the padding to 50%. To keep it short: the ratio of the container div's width and padding should always be equal to the ratio of the image's width and height.

---

There is an easy way to do exactly this, but it only works for square images.
Specify the width of the image (using CSS) to be 100%. This way the browser will automatically assume that the image height is the same as it's width, and preoccupy the place.

http://jsfiddle.net/pQ5zh/2/

.test-image {
    width:100%;
}

Note: There is a way to achieve this for non-square images too, but that is a bit more complicated.

EDIT: See above.