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.NET Forum / Languages / C# / February 2008Image verification
I am trying to generate an image on my login screen that the user must enter the characters of in order to login successfully. I have managed to find a method that returns a bitmap, but I am not sure how to render it to the page alongside the rest of the login page. Bitmap bmp = iv.generateImage(sTxt); Response.ContentType = "image/gif"; bmp.Save(Response.OutputStream, ImageFormat.Gif); bmp.Dispose(); I guess I will need to switch Response.ContentType to also show the rest of the page. What do I need to do to show both my image and the rest of the page on screen? Mike, What you need to do is have an IMG tag in the login page that will reference the page/URL that will dynamically generate the image. You will have to pass along any information in the URL that the page needs to generate the image.  Signature- Nicholas Paldino [.NET/C# MVP] - mvp@spam.guard.caspershouse.com >I am trying to generate an image on my login screen that the user must > enter the characters of in order to login successfully. I have managed [quoted text clipped - 13 lines] > > *** Sent via Developersdex http://www.developersdex.com *** Nicholas, If the image is being created on a separate page and then viewed through an Image control on the Login page, how do I get at the string that is created on the Image page so that I can verify that what the user types in matches the string? Hello Mike, > Nicholas, > > If the image is being created on a separate page and then viewed > through an Image control on the Login page, how do I get at the string > that is created on the Image page so that I can verify that what the > user types in matches the string? You can store it in the Session or the Viewstate. -- Jesse Houwing jesse.houwing at sogeti.nl Mike, Well, the login page is going to place the IMG tag in the page, right? And you are using Session State or something in the query string to indicate what the string used in the image should be. The login page should be generating this string, or the page generating the image should be placing it in session state (I don't like this, because you might have multiple requests in the same session hitting that variable, and it could cause issues). Either way, the login page is aware of the string already. I recommend that the login page generates the string, and then passes it to the page generating the image, using some sort of encryption key (I like generating a hash using the ASP.NET session id and then using that as an encyrption key across the session). Signature- Nicholas Paldino [.NET/C# MVP] - mvp@spam.guard.caspershouse.com > Nicholas, > [quoted text clipped - 4 lines] > > *** Sent via Developersdex http://www.developersdex.com *** Cheers! > Cheers! > > *** Sent via Developersdexhttp://www.developersdex.com*** The way I solved this was I used the Cache, stored my string in there with a short expiery and a GUID as a key. I passed the Guid to the handler to genarate the CAPTCHA image - the handler then retrieved the string from the Cache - minimal collision problems curtesy of Guid immense phase space. Isn't there more chance of winning every lottery on the planet or something? Your login page would be responsible for removing the string from the cache, but the cache will do it itself after... say... five, ten minutes? Long enough for the turboest of R-Type 'tards to work out what's going on. > I am trying to generate an image on my login screen that the user must > enter the characters of in order to login successfully. I have managed [quoted text clipped - 14 lines] > > *** Sent via Developersdex http://www.developersdex.com *** This piece of "technology" is called a CAPTHCA, so google for some examples. SignatureLasse Vågsæther Karlsen mailto:lasse@vkarlsen.no http://presentationmode.blogspot.com/ PGP KeyID: 0xBCDEA2E3 Mike, don't reinvent the wheel. Try this google search: http://www.google.com/search?q=ASP.NET+CAPTCHA+CONTROL -- Peter Site: http://www.eggheadcafe.com UnBlog: htp://petesbloggerama.blogspot.com Short Urls & more: http://ittyurl.net > I am trying to generate an image on my login screen that the user must > enter the characters of in order to login successfully. I have managed [quoted text clipped - 14 lines] > > *** Sent via Developersdex http://www.developersdex.com *** Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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