Are you still using the “Sharpen” Filter in Photoshop to try to improve the on-screen presentation of your photos?
There is a better way!
1) Sharpening is best done at the final output size, so first open your image in Photoshop, and scale it down to whatever size you want. For Flickr, 500 pixels wide is the size for the “medium ” option.
2) Go to the Layer palette, select your Background Layer, Right Click. Select Duplicate Layer.
3) With the new layer selected, goto Filter > Other > High Pass. Set the Radius to (probably) between 2 and 10. If you go too high, you’ll see a halo effect around the edges of your image. Back it down so the halo disappears. Click OK.
4) View your image at Actual size (Command + Option + 0 on a Mac)
5) From the Layer Palette, select Hard Light from the drop down menu. You can also select Soft Light or Overlay to see how those change your results.
6) Change the Opacity until the photo looks good to you. (Typically 25% to 75%).