Help with simple script.

For loop syntax is confusing, I tried researching and I still wasn't able to make sense of the syntax. This is a very simple script and it does the following:
1 > Recursively loop through current and subdirectories, finding .jpg files
2 > once found, simply do this command

echo. >> *.jpg

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And that's it
Here's what I've tried so far so that I don't look lazy.

@echo off
FOR /D %%a IN (*.jpg) DO (echo. >> *.jpg %%a)

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Code works without error but does not achieve what I want. The purpose of the

echo. >> *.jpg

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command is to simply send empty data to the jpg files so that the md5 is changed but without causing any problems to the picture itself