Posted: 01/08/2015 at 12:35
I find things work best if you keep the actual file size under 1MB. The two ways of doing that are to use a different jpeg compression level (better photo editors let you control when you save the images) and/or resize the images but doing that reduces the degree we can zoom-in to a posted photo. For a free solution which works great in Windows, try Irfanview: http://www.irfanview.com/
When you use Save As, there is a simple slider to change the jpeg compression level (labelled "Save quality.")
This is a 3072x2304 image saved at level 70 which produces a file size of 987KB:
As you can see, it's possible to zoom right in to the flowers.