[
    {
        "N": "3M",
        "a": "<img src="/img/samples/flag_red.gif" alt="red" height="16" width="16" border="0"/>",
        "c": "<img src="/img/samples/flag_red.gif" alt="red" height="16" width="16" border="0"/>",
        "r": "<img src="/img/samples/flag_red.gif" alt="red" height="16" width="16" border="0"/>",
        "p": "<img src="https://a.na7.visual.force.com/resource/1260007793000/a/iconset/gray.gif" alt=" " height="16" width="1" border="0"/>"

    },

    {
        "N": "ABC corp",
        "a": "<img src="/img/samples/flag_red.gif" alt="red" height="16" width="16" border="0"/>",
        "c": "<img src="/img/samples/flag_red.gif" alt="red" height="16" width="16" border="0"/>",
        "r": "<img src="/img/samples/flag_green.gif" alt="green" height="16" width="16" border="0"/>",
        "p": "<img src="https://a.na7.visual.force.com/resource/1260007793000/a/iconset/gray.gif" alt=" " height="16" width="1" border="0"/>"

    }
]

[
    {
        "N": "3M",
        "a": "red",
        "c": "red",
        "r": "red",
        "p": "gray"

    },

    {
        "N": "ABC corp",
        "a": "red",
        "c": "red",
        "r": "green",
        "p": "gray"

    }
]

var data = [{
    "N": "3M",
        "a": "<img src="/img/samples/flag_red.gif" alt="red" height="16" width="16" border="0"/>",
        "c": "<img src="/img/samples/flag_red.gif" alt="red" height="16" width="16" border="0"/>",
        "r": "<img src="/img/samples/flag_red.gif" alt="red" height="16" width="16" border="0"/>",
        "p": "<img src="https://a.na7.visual.force.com/resource/1260007793000/a/iconset/gray.gif" alt=" " height="16" width="1" border="0"/>"

}, {
    "N": "ABC corp",
        "a": "<img src="/img/samples/flag_red.gif" alt="red" height="16" width="16" border="0"/>",
        "c": "<img src="/img/samples/flag_red.gif" alt="red" height="16" width="16" border="0"/>",
        "r": "<img src="/img/samples/flag_green.gif" alt="green" height="16" width="16" border="0"/>",
        "p": "<img src="https://a.na7.visual.force.com/resource/1260007793000/a/iconset/gray.gif" alt=" " height="16" width="1" border="0"/>"

}];

var modified = data.reduce(function (outArr, entry) {
    var outObj = {};
    for (key in entry) {
        if (entry.hasOwnProperty(key)) {
            var item = entry[key];
            var node = document.createElement("div");
            node.innerHTML = item;
            var img = node.querySelector("img");
            outObj[key] = img ? img.alt : item;
        }
    }
    outArr.push(outObj);
    return outArr;
}, []); //[{"N":"3M","a":"red","c":"red","r":"red","p":" "},{"N":"ABC corp","a":"red","c":"red","r":"green","p":" "}]

var obj=[
{
    "N": "3M",
    "a": "<img src="/img/samples/flag_red.gif" alt="red" height="16" width="16" border="0"/>",
    "c": "<img src="/img/samples/flag_red.gif" alt="red" height="16" width="16" border="0"/>",
    "r": "<img src="/img/samples/flag_red.gif" alt="red" height="16" width="16" border="0"/>"
},
{
    "N": "ABC corp",
    "a": "<img src="/img/samples/flag_red.gif" alt="red" height="16" width="16" border="0"/>",
    "c": "<img src="/img/samples/flag_red.gif" alt="red" height="16" width="16" border="0"/>",
    "r": "<img src="/img/samples/flag_green.gif" alt="green" height="16" width="16" border="0"/>"
}
];

for(var k in obj){
    for (name in obj[k]) {
        if(obj[k][name].indexOf("<img") != -1) {
            // I have made logic based on "flag_", this can be change as per your requirement.
            var src= obj[k][name].substring(obj[k][name].indexOf("flag_")+5,obj[k][name].indexOf(".gif"));
            obj[k][name]=src;
        }
    }
}