ASP.NET image not loading, using imageHandler - asp.net

Question

I ran into a very annoying, and strange problem with loading pictures, using a custom handler (we need to mask the pictures runtime).
The Website, where you can check it out: http://utazovilag.hu/Test/Stack/Main.aspx
The basics: As I stated above, I use a custom image handler for loading and modifiding images at runtime. This site offer different travels, each changed frequently (changing the price, mostly). Each hotel have an own set of pictures, where we put an "advertisement" bar on it (a semi-transparent black rectangle, with some text). This handler load the image (some from the local server, some from another URL source), and draw the needed text and pictures on it, then give back the picture itself on the Response stream.
The error: The above should work well, but strangely, the pictures itself sometimes simply dont load at all. (if you check the site on the above link, you can see it for yourself - there should be six pictures, inside a rouded bluish border). When I refresh the page, pictures appear and disappear, without any (for me) logical pattern.
I narrowed down the problem as best as I could.
The imageHandler itself will give back the exatly same pictures each
time, no matter if it gets any URL or not.
The problem is with the ImageBoxes (I think). When I give the "plain"
url (one without any parameter, even when the handler dont even check
if there any parameter)
When I add the URL for the imageBoxes (this
one:http://utazovilag.hu/Test/GetTestImage.ashx) this will give the
perfectly good image back, and each imagebox will load without any
error.
When I add the URL with SAME parameters, its work like as it should
(like: http://utazovilag.hu/Test/GetTestImage.ashx?OID=0&PID=0&SID=0)
it works as it should.
(And now, the error) when I add an URL with different parameters, its make the pictures randomly pop up and dissapear between each refresh (this what you can see on the link I gave you above) Like this: http://utazovilag.hu/Test/GetTestImage.ashx?OID=0&PID=0&SID=0 And this: http://utazovilag.hu/Test/GetTestImage.ashx?OID=1&PID=0&SID=0
But when I hit the "Refresh Image" button, the image appear as it should. When I try to acces directly the GetTestImage.ashx, it appear as it should. The load problem only appear when there is more picture boxes, with different URLs.
I simply ran out from ideas, and cant imagine why is this happening. I tried to create the most basic imageHandler (it simply load the image, create byte array, and push that to a stream toward the user). I tried different browsers, (Firefox, IE, Chrome) - all of them give the same error (or, no error, as simply the picture not showing up).
Any ideas would be really-really appreciated.
Edit: Here is my imageHandler: http://pastebin.com/FjjUmNzW
Edit1: I forgot to mention it: it runs fine on my local machine, this error appear when I try to run it on the server.
Edit2: Updated the handler code as well, I showed where I put the log-asking.

Answer 1

Set the IsReusable property to true to handle multiple images. There is no MSDN documentation for this the last time I looked. But this is what I use for displaying say, a list of product images.
public bool IsReusable
{
get
{
return true;
}
}
Apparently, this keeps the handler in memory and able to handle multiple requests. When set to false, it had to create a new instance of the handler for each incoming request.