So you want to make a list of absolute URLs, like:
ftp://example.com/LeadImage/Pending/file1.jpg
ftp://example.com/LeadImage/Pending/file2.jpg
ftp://example.com/LeadImage/Pending/file3.jpg
??
using System.Linq;
using System.Text.RegularExpressions;
string[] files = Directory.GetFiles(@"\LeadImage\Pending\", "*.jpg", SearchOption.AllDirectories);
var URLs = from file in files
let f = file.Replace(@"\", "/")
select Regex.Replace(f, @"(^.+)(/LeadImage/Pending/.+)$)", "ftp://example.com$2");