Which xslt method are you using to show images? At the very least what xmlpackage, if you are using a stock xmlpackage. If it is
Code:
<xsl:value-of select="aspdnsf:LookupProductImage(ProductID, ImageFilenameOverride, SKU, 'medium', 0, $AltText)" disable-output-escaping="yes" />
That alt tag doesn't look to have an issue with large images in the code. There is a title set when there is a large image but the alt text is still there. If you want to change the title text it is just repacling line 2151 in the XSLTExtensionBase.cs with:
Code:
tmpS.Append("<img border=\"0\" id=\"ProductPic" + ProductID.ToString() + "\" name=\"" + CommonLogic.IIF(AppLogic.AppConfigBool("NameImagesBySEName") && !String.IsNullOrEmpty(seName), seName, "ProductPic" + ProductID.ToString()) + "\" style=\"cursor:hand;cursor:pointer;\" onClick=\"" + CommonLogic.IIF(ImgGal.HasSomeLarge, "popuplarge" + "_" + sProductID + "()", "popupimg('" + LargePicForPopup + "')") + "\" title=\"" + AltText.Replace("\"", """) + "\" src=\"" + ProductPicture + "\" alt=\"" + AltText.Replace("\"", """) + "\" />");