Android : ( html/css ) Png image not showing on iphone

I have an issue making a mobile version of a website due to a png image not showing on iphone only.

The page is very simple, just some div, a background and a transparent png behind the text.

This png weight ~180ko, it is already transparent and I modify the opacity again with css.

On my android phone it shows perfectly fine, but on an iphone, no image at all.

I've tested many ways but don't know where the issue come from, image size ? css property ? etc...

Here is the mobile website url : http://pianissimo-reze.fr/v2/mobile The png itself : http://pianissimo-reze.fr/v2/mobile/handm.png

and the html/css code :

<div id=photofond><img alt="" src="handm.png" /></div>



#photofond {
opacity: 0.5;
position: absolute;
top: 23%;
z-index: -1;
}

#photofond img {
width: 100%;
}

Thanks for your help !