how to release object from thid party dll

hi all,
i'm developing a program to convert RTF to html
i'm using the DLLs found here
http://www.codeproject.com/KB/recipes/RtfConverter.aspx?fid=1458864&df=90&mpp=25&noise=3&sort=Position&view=Quick&select=3427424&fr=1#xx0xx

this dll saves a jpd file from html to a specific folder,
when i run the program, it cinverts the rtf for the first time and saves the images to the folder perfectly
but when i try to convert it again i hace this error
"error a generic error occured in GDI+"
i think this dll use SaveImage method and to avoid this you must release the Image object you created but i can't modify the DLL,
is there is any way to release the object i've created from this dll?
this is my code

RtfVisualImageAdapter imageAdapter = new RtfVisualImageAdapter(@Application.StartupPath + "\\Program Data\\temp\\{0}{1}", System.Drawing.Imaging.ImageFormat.Jpeg);
            RtfImageConvertSettings imageConvertSettings = new RtfImageConvertSettings(imageAdapter);
            RtfImageConverter imageConverter = new RtfImageConverter(imageConvertSettings);
           
            try
            {
                IRtfDocument rtfDocument = RtfInterpreterTool.BuildDoc(ConversionText, imageConverter);
                RtfHtmlConverter htmlConverter = new RtfHtmlConverter(rtfDocument);
                htmlConverter.Settings.ConvertVisualHyperlinks = true;
                htmlConverter.Settings.UseNonBreakingSpaces = true;
                this.richTextBoxPrintCtrl2.Text = htmlConverter.Convert();
            }
            catch (Exception exception)
            {
                MessageBox.Show(this, "Error " + exception.Message, this.Text, MessageBoxButtons.OK, MessageBoxIcon.Error);
            }

 i just need to dispose these objects but the DLL doesn't implement the dispose method

thanks in advance for any replies