Thumbnail tutorial - Photoshop
1. Open the image you plan to make a thumbnail of.
2. Make sure the image is in Grayscale or RGB mode. You can check this by clicking on image in the menu bar, then mode - there will be a check mark next to the mode your are currently in. GIF images, for example, will be in indexed color mode when you open them. Select RGB for color images, and grayscale for black and white ones.
3. Click on the marquee tool in the toolbar. Make sure that the rectangular marquee tool is selected - click and hold down the mouse button to select a different tool.
4. Use the marquee tool to select the area of your image you want to make into a thumbnail.
5. Go to image in the menu bar, then crop.
6. To change the size of your thumbnail, select image from the menu bar, then Image size. A new window will pop up. Make sure that constrain proportions (constrain aspect ratio in 5.5) and resample image are both checked. Also, check to make sure that the resolution of your image is 72.
To change the size of your image, click on one of the top two boxes and enter a new width or height. Generally, thumbnails should be no more than 100 pixels high or wide.
When youre done, click OK.
7. If your thumbnail looks like you want it to, click on File in the menu bar, then save as. Type in a name for your thumbnail (like image_tn.jpg), select JPEG as your format, and click ok.
Another window will pop up, asking you to set the quality of your jpeg. For most thumbnails, setting the quality at medium and the format as baseline optimized will be fine. Click ok again, and youre done!