You can combine criteria with
-o as suggested by Shadur. Note that
-o has lower precedence than juxtaposition, so you may need parentheses.
find . -name '*.jpg' -o -name '*.png'
find . -mtime -7 \( '*.jpg' -o -name '*.png' \) # all .jpg or .png images modified in the past week
On Linux, you can use
-regex to combine extensions in a terser way. The default regexp syntax is Emacs (basic regexps plus a few extensions such as
\| for alternation); there's an option to switch to extended regexps.
find -regex '.*\.\(jpg\|png\)'
find -regextype posix-extended -regex '.*\.(jpg|png)'
On FreeBSD, NetBSD and OSX, you can use
-regex combined with
-E for extended regexps.
find -E . -regex '.*\.(jpg|png)'