I use a program called "GIMP" to mess with pictures. It's free! This does most of what Photoshop does - the stuff we generally need anyway (I don't have much use for YCM colorspace...).
To resize a phot in gimp, open it and on the window with the pisture select the "image" tab, and "scale image". The top set of numbers are the size, probably shown as pixels (change to pixels if it's inches or whatever). The chain image beside/betwenn the two numbers should be linked, click it to link if it shows as broken. Change the top number to maybe 640 (a standard picture size for landscape oriented images), when you hit "enter" the other number should change to something close to 480. In the bottom of the scaling window change the "quality" to "cubic (best)". Click "scale".
Now "file", "save as" the resized image - use "save as" or your original image will be overwritten. Click on "select file type by extension", choose "jpeg". Click "save" and you will probably see a window about exporting before converting to jpeg - either "flattening" (?) the image or going to RGB or greyscale, pick RGB for colour images or greyscale for B&W. Click "export" and you get a window to select jpeg compression quality, the file size gets bigger with higher percentage quality but the image looks pretty ratty below 50%, 85% is good - check the filesize after saving and resave with a lower percentage if still too high.
You can play with the image in a lot of ways, changing contrast and such too. I usually adjust the images using "tools", "color tools", "levels" to get a nice bright well contrasted image for posting. Messing with the "curves" just ruins the picture in my experience.
