I checked the GDL Manual. There is a PICTURE command for placing images in 3D, and there is a PICTURE2 command for placing pictures in 2D. You would probably need the PICTURE2 command.
However, it seems to me that alpha channel is very limited in the PICTURE2 command. It has a variation, the PICTURE2{2} command, which makes it posibble to use the alpha channel for transparency, but that is all.
If you have A and B as the two main parameters of the Object, then its width and height can be scripted to be set by these parameters and so you can distort it any way you like.
If you want it to be like 1 meter (1 meter is the project not on paper) at all scales, that will happen by default. If you want it to be something like 100 millimeters (always 100 millimeters on paper) at all scales, then you will have to use the GLOB_SCALE variable of GDL to resize it depending on the current scale.
The name of the external picture file has to be a parameter string-type. Check the Picture 11.gsm file so see how it is done. I don't knowright now if you can give a full path tho the file's location or it must be in the loaded libraries and you can just give the file name.
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