If you modify the localization text for captcha under languages->SharedResources

you will want to change Resource Name: Captcha.Help, Captcha.Text, CaptchaText.Text, InvalidCaptcha.Text

This will change the text in all but under registration.

The localization code for this resource is under admins\users\user.aspx.vb under the databind event. For some reason this is not working for captcha.

Solution modify this file to include localization code for captcha under the page_load event.

Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

            UserEditor.LocalResourceFile = Me.LocalResourceFile
 
            If UseCaptcha Then
                ctlCaptcha.ErrorMessage = Localization.GetString("InvalidCaptcha", Localization.SharedResourceFile)
                ctlCaptcha.Text = Localization.GetString("CaptchaText", Localization.SharedResourceFile)
            End If

End Sub