Click the Text tag and type in the text you want in the Caption box. Make sure image captioning is switched on and the button in the top right shows: Image Optimizer on Adding a text caption 

You can use the following characters to include information in the caption:

+p  file path
+f filename
+e extension
+it File Time (hh:mm)
+id File date (dd-Mmm-yy)
+t time (hh:mm)
+d date (dd-Mmm-yy)
+x EXIF data, see below
+a IPTC data, see below
++ +

Click the Image Optimizer textstylebutton Adding a text caption button to set the font style and size. Click the “Fore” button set set the color of the text. If you want a background click the check box and click the “Back” button to select a background color.

Set your required location, opacity and margins.

If you want a drop shadow background click the “DrSha” check box. The 3 boxes below control the size and position of the drop shadow.

Caption Image Control Palette

Adding an image or visible watermark

Full list of codes available including EXIF and IPTC

+n Newline (for multi-line text)
+p  File path
+f Filename
+e File extension (eg JPG)
+t Current time (hh:mm)
+d Current date (dd-Mmm-yy)
+it File Time (hh:mm)
+id File date (dd-Mmm-yy)
+xt EXIF Time (hh:mm)
+xd EXIF date (dd-Mmm-yy)
+xc EXIF Comment
+xe EXIF Description
++ +
+a5 IPTC Object Name
+a15 IPTC Category 
+a20 IPTC Supplemental Category
+a25 IPTC Keywords
+a40 IPTC Special Instructions
+a55 IPTC Date Created
+a60 IPTC Time Created
+a90 IPTC City
+a92 IPTC Street
+a95 IPTC State
+a100 IPTC Country Code
+a101 IPTC Country
+a105 IPTC Headline
+a110 IPTC Credit
+a115 IPTC Source
+a116 IPTC Copyright Notice
+a118 IPTC Contact
+a120 IPTC Caption/Abstract
+a122 IPTC Writer/Editor

Note all the IPTC data is available and can be accessed by using +aNNN where NNN is the code number. Where IPTC data has multiple values these are joined together and separated by a “;”

Adding a text caption