Finally someone has already made a good solution for this.
There is a good function of PHP, json_decode()
.
It converts that string (which I have learned later that it is JSON) into a key-value array. So all the data gets reachable:
$pictures = json_decode('{"image_intro":"images\/products\/201191420496.jpg",
"float_intro":"",
"image_intro_alt":"",
"image_intro_caption":"",
"image_fulltext":"",
"float_fulltext":"",
"image_fulltext_alt":"",
"image_fulltext_caption":""
}',
true);
echo $pictures['image_intro']; //gives images/products/201191420496.jpg