Question: Do Perl, Python or Ruby run flawless on a 64bit Win7 system, or do you have to keep in mind pitfalls with integers and restriction on functions like I have read of on PHP?

Answer: 
Another trick would be to have two img tags, and hide one depending on the device. 

HTML

```
<img id="img1" src="images/arts/IMG_1447.png" alt="">
<img id="img2" src="images/arts/IMG_1447m.png" alt="">

```

CSS

```
#img1 {display:block;}
#img2 {display:none}

@media all and (max-width: 499px) {
    #img1 {display: none;}
    #img2 {display: block;}
}

```
Updated: Please have a look at <http://jsfiddle.net/p96denv4/2/>

Here's what you would do. 

HTML

```
<div id="ifMobile1"></div>

```

CSS

```
#ifMobile1 {
    background-image: url(/images/arts/IMG_1447m.png)
    width: set your width  ;
    height: set your height  ;
}

@media all and (max-width: 499px) {
    #ifMobile1 {
        background-image: url(/images/arts/IMG_1447.png)
        width: set your width  ;
        height: set your height  ;
    }
}

```