а READ_IMAGE_FILE в триггере на вход в строку или элемент не поможет в таком случае?

пример из доки как раз подходит на мой взгляд:

/* Read an image from the filesystem into an image item on the

** form. In this example, the scanned picture identification
** for each employee is NOT saved to the database, but is
** stored on the filesystem. An employee's photo is a TIFF
** image stored in a file named <Userid>.TIF Each employee's
** Userid is unique.
** Trigger: Post-Query
*/
DECLARE
tiff_image_dir VARCHAR2(80) := '/usr/staff/photos/';
photo_filename VARCHAR2(80);
BEGIN
/*
** Set the message level high so we can gracefully handle
** an error reading the file if it occurs
*/
:System.Message_Level := '25';
/*
** After fetching an employee record, take the employee's
** Userid and concatenate the '.TIF' extension to derive
** the filename from which to load the TIFF image. The EMP
** record has a non-database image item named 'EMP_PHOTO'
** into which we read the image.
*/
photo_filename := tiff_image_dir||LOWER(:emp.userid)||'.tif';

/*
** For example 'photo_filename' might look like:
**
** /usr/staff/photos/jgetty.tif
** ------
**
** Now, read in the appropriate image.
*/

READ_IMAGE_FILE(photo_filename, 'TIFF', 'emp.emp_photo');
IF NOT FORM_SUCCESS THEN
MESSAGE('This employee does not have a photo on file.');
END IF;
:SYSTEM.MESSAGE_LEVEL := '0';
END;