library(rtweet)
library(dplyr)

neilfws <- get_timeline("neilfws", n = 100)
neilfws %>%
  glimpse()

neilfws %>%
  filter(!is.na(media_id) %>%
  nrow()

neilfws %>%
  filter(!is.na(media_id)) %>%
  select(media_url) %>%
  head()

1 http://pbs.twimg.com/media/DHzGbvyVoAAm8in.jpg
2 http://pbs.twimg.com/media/DHfc4idV0AA6qyc.jpg
3 http://pbs.twimg.com/media/DHfNamEVYAA5H_U.jpg
4 http://pbs.twimg.com/media/DHYuG1oUwAADV-z.jpg
5 http://pbs.twimg.com/media/DHQlEQqUAAAHoCK.jpg
6 http://pbs.twimg.com/media/DHLG_ESUMAAMURj.jpg