This package depends on rstudioapi, I don't think it can work without Rstudio. If you don't use Rstudio, grab_clipboard may be help for you: it grab image in clipboard and save to a local path.
In Rstudio, Tools -> Modify Keyboard Shortcuts -> RmdImgPaste,Customize a shortcut (for example, cmd + v, if not conflict), then you can just use 'cmd + v' paste image into a blogdown post or a Rmd file.
in macos, exec script like this:
osascript -e '
set theFile to (open for access POSIX file "test.png" with write permission)
try
write (the clipboard as «class PNGf») to theFile
end try
close access theFile'
in window (for 'windows7', 'powershell' need updated to 5.1):
powershell -sta '
Add-Type -AssemblyName System.Windows.Forms;,
if ($([System.Windows.Forms.Clipboard]::ContainsImage())) {
[System.Drawing.Bitmap][System.Windows.Forms.Clipboard]::GetDataObject(
).getimage().Save("test.png", [System.Drawing.Imaging.ImageFormat]::Png)
}'
in linux (xlip is needed):
xclip -selection clipboard -t image/png -o > "test.png"
if this Addin not work, you can test if this scipt can can generate test.png file when you have a image on clipboard
for a general Rmd files, all paste image in curr_path/.assets/, named like rmd-img-paste-%Y%m%d%H%M%s.png
for a blogdown post(.Rproj have somethin like BuildType: Website and in content/post), all paste image in static/post/postname_files/, and
insert code like 
this code is based on https://github.com/Timag/imageclipr and make some changes:
Add the following code to your website.
For more information on customizing the embed code, read Embedding Snippets.