Hi, so practicing some web development code and the part im stuck on is when a button is clicked it changes to picture and the caption is supposed to change. However no matter what i try the caption remains the same.
The following is part of the code i have.

function showImage(imageFileName) 
    // get image element
    var theImageElement = document.getElementById("cameraImage");
    // change what image is displayed

    if(cameraImage= "Canon_20d.jpg")       
    document.getElementById("imageCaption").innerHTML = "Canon 20d";
    else if(cameraImage= "Fuji_s3Pro.jpg")     
    document.getElementById("imageCaption").innerHTML = "Fuji S3 Pro";
    else if(cameraImage= "Fuji_9500.jpg")      
    document.getElementById("imageCaption").innerHTML = "Fuji 9500";
    else (cameraImage= "sony_r1.jpg")      
    document.getElementById("imageCaption").innerHTML = "Sony r1";
<div id="mainContainer">
    <div id="topSection">
        <h1 style="text-align:center; padding-top:20px">COM301 Recipe 7: Camera e-commerce site</h1>
    <div id="contentWrapper">
        <div id="contentLeft">
            <p style="text-align:center">Useful Links</p>
            <br />
            <a href="http://www.google.com">Click here for Google</a>
            <br />
            <a href="http://www.bbc.co.uk">Click here for BBC</a>
            <br />
            <div id="contentRight">
        <div style="float:right; margin-top:5px; margin-right:5px">
        <img id="cameraImage"  src="blank.jpg" /> <br />
        <div style="text-align:center" id="imageCaption"> No Image</div>
                // open a file for reading
                $fp = fopen("cameras.txt", "r");
                if ($fp != FALSE) {
                    // set up the table for structured output
                    echo "<table border='2' width='75%' rows='4'>";
                    echo "<tr><th>Make</th><th>Model</th><th>Price</th><th>Rating</th><th>Stock</th><th>Image</th></tr>";
                    // read the data line by line
                    while (($buffer = fgets($fp)) != FALSE)  {
                        // extract the component parts of the line
                        // remove whitespace
                        $buffer = trim($buffer);

                        $data = explode(',', $buffer);
                        // display the data
                        echo "<tr><td align='center'>$data[0]</td>
                        <td align='center'>$data[1]</td>
                        <td align='center'>$data[2]</td>
                        <td align='center'>$data[3]</td>
                        <td align='center'>$data[4]</td>
                        <td align='center'><input type='button' value='Image' onClick='showImage(\"$data[5]\");'/></td></tr>";  
                    // close table
                    echo "</table>";
                    // close the file

Anyone any idea how i can get the caption to change that appears beneath the picture. Thanks in advance.

The way you use your condition is wrong. One equal sign means "assign" but two equal sings means "comparison" of 2 values. In your case cameraImage= should be cameraImage==.

Thank you, never even realised i only had one there.