My two cents
On the rare occasions I need to insert an image I need to downsize the resolution to reduce the file size as the site will only allow a limited file size. There are plenty of free downsizing sites on the web. Most folks use cameras that take high resolution shots and they are a way too large file size so they need to downsize them before attaching an image.
Two more cents:
The ImageMagick package (free and runs on the usual popular OSes) contains the convert command which can resize an image.
http://www.imagemagick.org/
How to reduce file size ("%" is the command prompt, my comments are in parenthesis):
% identify original_file.jpg
(returns the file type and size, divide the size by the desired factor)
% convert original_file.jpg -resize new_size shrunken_file.jpg
An example (to halve the dimensions of a file, UNIX/Linux syntax):
% identfy IMG_30084.jpg
IMG_3084.jpg JPEG 6000x4000 6000x4000+0+0 8-bit sRGB 4.606MiB 0.010u 0:00.009
(size is 6000x4000, half size is 3000x2000)
% convert IMG_3084.jpg -resize 3000x2000 output_3084.jpg
Convert and the rest of the ImageMagick package can also do many other things. (I use it frequently...) Reducing the "quality" (compression level) of a JPEG can also shrink the file size. (Convert can do this too.)
Doug