Here is a method To print over images: taken from here. Use a different layer for your text you're putting over the images, and also make sure to use the GetOverContent() method.
string oldFile = "FileWithImages.pdf";
string watermarkedFile = "Layers.pdf";
// Creating watermark on a separate layer
// Creating iTextSharp.text.pdf.PdfReader object to read the Existing PDF Document
PdfReader reader1 = new PdfReader(oldFile);
using (FileStream fs = new FileStream(watermarkedFile, FileMode.Create, FileAccess.Write, FileShare.None))
// Creating iTextSharp.text.pdf.PdfStamper object to write Data from iTextSharp.text.pdf.PdfReader object to FileStream object
using (PdfStamper stamper = new PdfStamper(reader1, fs))
{
// Getting total number of pages of the Existing Document
int pageCount = reader1.NumberOfPages;
// Create New Layer for Watermark
PdfLayer layer = new PdfLayer("Layer", stamper.Writer);
// Loop through each Page
for (int i = 1; i <= pageCount; i++)
{
// Getting the Page Size
Rectangle rect = reader1.GetPageSize(i);
// Get the ContentByte object
PdfContentByte cb = stamper.GetOverContent(i);
// Tell the cb that the next commands should be "bound" to this new layer
cb.BeginLayer(layer);
BaseFont bf = BaseFont.CreateFont(BaseFont.HELVETICA, BaseFont.CP1252, BaseFont.NOT_EMBEDDED);
cb.SetColorFill(BaseColor.RED);
cb.SetFontAndSize(bf, 100);
cb.BeginText();
cb.ShowTextAligned(PdfContentByte.ALIGN_CENTER, "Some random blablablabla...", rect.Width / 2, rect.Height / 2, - 90);
cb.EndText();
// Close the layer
cb.EndLayer();
}
}