I don’t do a lot of image processing. The image processing that I have done is with TIFF. So, I’ll talk in terms of TIFF.
The BLOB spray will create a record for each image file. The record that you create can be a string for the file name and a variable length DATA (a byte sequence). The variable length DATA field is the file content.
The TIFF content has some descriptive data fields followed by the image. The image is a row major matrix.
I don’t recall if the descriptive fields are fixed width, but if not you can write an attribute in C++, Java, Python, or R that breaks the matrix out.
It is possible to convert the TIFF dataset with only ECL, but you really need to know a lot about the ECL data manipulation features. For most people, it is more straight forward and just as efficient to do the extraction in C/C++ attributes.