Home Forums Gear Photography Compressed pictures...

Your 640 pixel wide image is going to lose some sharpness if it is enlarged to fit the image spot on the page. As 1' suggests, save at a larger size. I save images for forums at 1400 pixels and upload to postimages.org to link in the forum posts. You might try saving at 800, 1200, 1400 pixels, etc and compare how the different images look to you on the web. Did you use flikr as a host? What image size have you chosen to save as on flikr, if is gives you an option?
Save the files slated for the web in sRGB color space as AdobeRGB and ProPhotoRGB will show with flatter colors on the web.
If a large file is posted and compressed in size for the web, you may get halos along object edges, so you might sharpen your web files after downsizing for web to avoid halos.