specify 2 filetypes (endings) for a “for loop”?

You can use syntax like the following:

for f in /tmp/*.{jpg,png}; do
    echo "filename: $f"
done

Update:

For better handling of the case when there is no file matching the pattern, you might try Pathname Expansion instead of Brace Expansion:

for f in *[email protected](jpg|png); do
    echo "filename: $f"
done

From what I understand, Brace Expansions can expand to file names that don’t exist, while Pathname Expansions…can…not…?