Please be very careful with this, there is no safety net to catch you.
If all the 100 folders are inside folder x then open a command window and CD into folder x and then
erase /p /s *.jpg
That /p is going to prompt you to ask whether you want each file erased or not. I would suggest looking carefully at the name of the file it is about to erase and answering no to that question again and again and again until it is done. If every one of those file names was correct and it didn't end up asking you if you wanted to erase a very important file that you wanted to keep then you can do
erase /s *.jpg
and let it go.
All this is based on reading
https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/erase
The /s will have it look into the x folder, erase all jpg files there and then go into every folder inside x and do the same and go into every folder in every folder inside x, etc.
Ah, there is another way.
Windows Explorer is what you may use when you are trying to find files. You can use that to move to your x folder and then use the search box that is in the upper right corner to look for all jpg files in x and below x. That will take a while to complete. That should show you a list of every jpg file in those folders. Then you can carefully look through all the buttons across the top of the window and find a button that will Select All of those search results. That should highlight all the 100 plus jpg files. Then more looking through the buttons and you should find a red X with a Delete label under it. Tapping on that X should move all those highlighted file names to the Recycle Bin. (There are settings to make anything deleted to be instantly permanently deleted, presumably you have not set that. There are also things like if you do this from an inserted thumb drive that the deleted files do not go to the recycle bin on the thumb drive, because there isn't one, presumably you are not doing this from a thumb drive. After all those cautions... (Can you tell I don't trust not losing important files?) Then you are free to close Windows Explorer, open the Recycle Bin, see that all the appropriate files are there and then empty the bin.
Please post a message when you are done and let everyone know how it worked for you