What does mean ECG? is it electrocardiogram? Can you post 1 ECG for us to try something on it?
I do know BIMP and David's batch processor, but I'm not aware of "Batch GIMP", can you provide a link to test?
20 000 photos... I won't try with GIMP at first, I'll try with the few effect that propose XnConvert, if I can get something decent (anyway you just want to degrade pictures), or try one photo in GIMP simplify the process and try to reproduce it with XnConvert, then batch the 20 000 in XnConvert, just because speed wise, I don't want my computer computing for a day or more to batch 20 000 pictures in GIMP, when it can be done, maybe, in less than an hour with XnConvert.
XnConvert can use mask/superimposed picture, which allows a lot of things to do.
I do know BIMP and David's batch processor, but I'm not aware of "Batch GIMP", can you provide a link to test?
20 000 photos... I won't try with GIMP at first, I'll try with the few effect that propose XnConvert, if I can get something decent (anyway you just want to degrade pictures), or try one photo in GIMP simplify the process and try to reproduce it with XnConvert, then batch the 20 000 in XnConvert, just because speed wise, I don't want my computer computing for a day or more to batch 20 000 pictures in GIMP, when it can be done, maybe, in less than an hour with XnConvert.
XnConvert can use mask/superimposed picture, which allows a lot of things to do.