how to tell if a url is for default blue image gravatar - gravatar

Question

Is there a way to tell if a url is for default blue gravatar image?
Here are two urls for the default Gravatar image:
http://www.gravatar.com/avatar/19b2990ba88512ab38abdbbca5701d27?s=120
http://www.gravatar.com/avatar/88a771dc1a611b2038c9a0ad0770b595?s=120
Here is a url that has an image:
http://www.gravatar.com/avatar/d8f98df8a6ed24a727b993ea01cc91f6?s=120
Is there something in these url's that I can search for that the default blue gravatar image url has that the non default gravatas do not have?
Edit:
What I am trying to do is:
I have an excel sheet downloaded from an app that has a column for gravatar urls. I need to delete all the links that go the the default blue gravatar image.

Answer 1

Gravatar avatar image URLs that are the default image will return a 404 Not Found error if the following parameter is set d=404. For example, here are the URLs that you used as examples, but with the parameter set:
http://www.gravatar.com/avatar/19b2990ba88512ab38abdbbca5701d27?s=120&d=404
http://www.gravatar.com/avatar/88a771dc1a611b2038c9a0ad0770b595?s=120&d=404
http://www.gravatar.com/avatar/d8f98df8a6ed24a727b993ea01cc91f6?s=120&d=404
Assuming you're detecting if the images default using JavaScript, you can then use AJAX (without displaying the image) or an error catcher (displaying non-default images) to detect if these images successfully loaded.
jQuery (AJAX)
// Image Exists
$.ajax({url:"http://www.gravatar.com/avatar/d8f98df8a6ed24a727b993ea01cc91f6?s=120&d=404",type:"GET",crossDomain:true,success:(function(){console.log("Custom Gravatar");}),error:(function(){console.log("Default Gravatar");})});
// Image Does Not Exist
$.ajax({url:"http://www.gravatar.com/avatar/88a771dc1a611b2038c9a0ad0770b595?s=120&d=404",type:"GET",crossDomain:true,success:(function(){console.log("Custom Gravatar");}),error:(function(){console.log("Default Gravatar");})});
Error Catching
You can use either the jQuery load and error event handlers, or the HTML onload and onerror attributes.
$("img").load(function(e) {
e.target.parentNode.parentNode.getElementsByClassName("stat")[0].innerHTML = e.type;
}).error(function(e) {
e.target.parentNode.parentNode.getElementsByClassName("stat")[0].innerHTML = e.type;
});
table,
td {
border: 1px solid black;
border-collapse: collapse;
}
table img {
width: 48px;
height: 48px;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<table>
<tbody>
<tr>
<td>Image</td>
<td>Expected Result</td>
<td>Actual Result</td>
</tr>
<tr>
<td>
<img id="good" src="http://www.gravatar.com/avatar/d8f98df8a6ed24a727b993ea01cc91f6?s=120&d=404" />
</td>
<td>load</td>
<td class="stat">Loading...</td>
</tr>
<tr>
<td>
<img id="bad" src="http://www.gravatar.com/avatar/88a771dc1a611b2038c9a0ad0770b595?s=120&d=404" />
</td>
<td>error</td>
<td class="stat">Loading...</td>
</tr>
</tbody>
</table>
EDIT: OP clarified what was being asked for
I wrote a small VBA script in this example file to iterate through the first column up until the first empty cell, creating WinHTTP requests with a modified URL then, as OP asked, deleting the contents of cells that contained a link to the default Gravatar avatar.
To run the code in the sample Excel file:
Excel 2003 and lower: Tools > Macro > Macros (Alt + F8) > checkGravatar
Excel 2007 and newer: Develooper > Macros > checkGravatar
In order to run the VBA, you may also need to enable macros and reference MSXML.
Sub checkGravatar()
Set objHTTP = CreateObject("WinHttp.WinHttpRequest.5.1")
Dim URL As String
Dim goodStat As String
Dim badStat As String
Dim row As Integer
Dim pos As Integer
row = 1
URL = Cells(row, 1).Value
Do While Len(URL) > 0
If InStr(URL, "gravatar.com/avatar/") > 0 Then
If InStr(URL, "?") = 0 Then
URL = URL & "?d=404"
Else
If Not InStr(URL, "&d=") Then
URL = URL & "&d=404"
End If
End If
objHTTP.Open "GET", URL, False
objHTTP.send ("")
If objHTTP.Status = 404 Then
Cells(row, 1).Value = ""
Else
MsgBox "GET request failed"
End If
row = row + 1
URL = Cells(row, 1).Value
Loop
End Sub

Answer 2

You can try to pass a default image of your choice, and see what is returned.
URLs mapping to existing gravatars will ignore the default image parameter, returning an image.
URLs mapping do no images will use the default you provide (instead of the blue G).
If you pass something invalid (empty string), you'll get a 400.
Compare the existing one:
http://www.gravatar.com/avatar/d8f98df8a6ed24a727b993ea01cc91f6?d=%22%22
With the non-existing one:
http://www.gravatar.com/avatar/19b2990ba88512ab38abdbbca5701d27?d=%22%22
That said... It's quite rude to deliberately cause errors on someone else's API.
You could fire off some background worker that will GET the images and see what's returned.