There is no way how a pictures like JPEGs could be converted to MP4 audio. However MPEG-4 (.mp4) is a container for multimedia content, including video or audio and may also contain images.
You can find presentation programs with which users my prepare videos that are like slideshows of images with audio playing in background, similar to what you can see on Youtube.
Other programs can be used to create a video sequence from multiple programs, but that generally uses a special format and not standard multimedia content.