HTML image view issue

HTML image view issue

Good day I have an HTML output where I need to display a image for a signature, I already have the link for the signature but when I display with the HTML img src I can't show correctly.

for each x in FetchRegistro
{
link = x.Firma_Url;
LinkFirma = "<img src='" + link + "' alt = 'test' height='30%'/>";
output = output + "<tr class='rowVal'><td>" + LinkFirma + "</td></tr>";
}

If I replace link with a sample value of the Firma_Url it works
LinkFirma = "<img src=" + " https://creator.zoho.com/czambrano1/recursohumano/Firma_Diaria_Report/2357982000002871223/Firma/image-download/1426707525078_signature.png" + " alt = 'test' height='30%'/>";

If I use without img src it works but of course I can't reduce the image size
link = x.Firma_Url;
output = output + "<tr class='rowVal'><td>" + link + "</td></tr>";


Its a quotes problem but actually I can't solved

Thank you,