Find all files with the extension ".gif" in the current directory and its subdirectories up to a maximum depth of 3, and execute the command "sed 's/[0-9]\+/[A-z]\+/g' {}" on each of them.
find -maxdepth 3 -type f -name "*.gif" -exec sed 's/[0-9]\+/[A-z]\+/g' {} \;