Move file, change permissions and rename it keeping the same extesion - permissions

Question

Using zsh 5.2 on Fedora 24 workstation.
I want to be programatically able to:
move an image file (can have jpg/ jpeg/ png/ JPG/ PNG extensions)
from /tmp/folder1 to ~/Pictures
This file will have the same few initial characters --- prefix111.jpg OR prefix222.png, etc.
rename the file such that samefilename.JPG becomes 20161013.jpg
20161013 is today's date in yyyymmdd format
Note that the extension becomes small letters
And JPEG or jpeg becomes jpg
change the permissions of the moved file to 644
All at one go.
If there are multiple prefix* files, the command should just fail silently.
I will initially like to do it at the command prompt with an option to add a cron job later. I mean, will the same zsh command/ script work in cron?
I am sure, this is doable. However, with my limited shell knowledge, could only achieve:
mv /tmp/folder1/prefix-*.JPG ~/Pictures/$(date +'%Y%m%d').jpg
Problems with my approach are many. It does not handle capitalization, does not take care of different extensions and does not address the permission issue.

Answer 1

How about this:
#!/bin/sh
FILES="/tmp/folder1/prefix*.jpg /tmp/folder1/prefix*.jpeg /tmp/folder1/prefix*.png h/tmp/folder1/prefix*.JPG /tmp/folder1/prefix*.PNG"
if [ $(ls $FILES | wc -l ) -gt 1 ]; then
exit 1
fi
if [ $(ls $FILES | grep -i '\.png$') ]; then
SUFF=png
else
SUFF=jpg
fi
DEST=$HOME/Pictures/$(date +'%Y%m%d').$SUFF
mv $FILES $DEST
chmod 644 $DEST