Image File Sizes

These are best understood as two separate concepts:
File Size is the amount of space a file occupies on disk, and is measured in kilobytes or megabytes.
Image Size is the length x width dimensions of an image, and is measured in pixels (when viewed onscreen) or in centimetres/inches (when printed on paper).
For the sake of people who still have a slow dial-up Internet connection, it would be nice to keep BugGuide file sizes to a minimum (say, 50 kilobytes or less) so the files don't take ages to upload to the BugGuide server - and download to a user's web browser.
File size can be reduced in any image-editing program, either by converting the file format (say, from an uncompressed TIFF format to a compressed JPG format) or by re-saving a JPG file in a lower quality/higher compression state. I always capture digital images at the camera's highest quality setting, then re-save copies of the originals at 75% JPG quality for onscreen viewing. Depending upon the complexity of the image, this translates to a 60-90% reduction in file size (example: a one megabyte file becomes 100-400 kilobytes).
Working on the image size is a separate issue. For small insects that don't come close to filling the frame, I crop (cut out) large sections of background, leaving the insect untouched in the middle of the frame. Of course, removing useless background pixels can result in the file size becoming "too small", as Eric mentioned, but that's unavoidable; my current camera equipment simply can't produce large-dimension images of tiny insects.
For larger insects that fill most of the frame, I resize the image, reducing its longest dimension to 560 pixels to accommodate BugGuide guidelines. 560 is a good number: any more than this would force people who have small monitors and/or 640x480 resolution to scroll sideways to view the rest of the image (remember that scrollbars, sidebars, & toolbars also take up screen space; even with the more common 800x600 monitor resolution, a maximum image width of 560-600 pixels is preferable).
All this editing is done with a COPY of the original photo. The original remains on my hard drive for future printing or other use. Every month, the previous month's photos are copied to CDs (don't have a DVD burner yet) and added to the collection stored at a relative's house, so I won't lose everything the day our house burns down.

Most of the images I've posted here have been prepared to look their best in the web format Troy provides here. I crop and resize the images, and apply filtering as necessary, specifically for the ~550 pixel format here. Some images which look good on the web may not translate into good print images.

I'm becoming a better bug photographer through practice, but it's sometimes difficult to fill the whole camera frame with the bug. Often I can crop the image significantly (losing lots of pixels in the process) and still get something usable for this website. My camera shoots 3072x2084 pixel images (~6 megapixel), which means I could crop away ~80% of the width and still post a ~550 pixel-wide image. Obviously I don't want to do that, but I had to in a lot of my early images because I didn't even have a macro lens back then. Lately I'm keeping a lot more of the frame.

Troy, I know your server stores the full size images and resizes them for the default display. What sort of method/software do you use to do the resizing, and do you run any filters during that process? I may have to play around with posting larger sizes. As an editor, it would be a cool feature if there was a little icon that would note when the "source" image was > 560 pixels (or maybe even tiny text giving the dimensions).

Just to be clear, Eric is talking about print size and isn't referring to the size of images uploaded to this web site. The images he refers to were submitted by the photographers separately after first being found on this website. Those files would have been larger than the ones here.

As for the site, you are free to upload any size you wish, but I prefer images to be 560 pixels on the longest side. Anything smaller just looks small and is more likely to be removed. Anything bigger gets resized down for normal viewing. If you submit something bigger, the original is preserved and editors have access to it, which might make it easier to make out fine details.

Most often, images I submit for publication are printed at 300dpi (dpi=dots per inch). So if you submit an image that's 300 pixels wide, then it'll be exactly 1 inch wide on the page. The desired printed size varies of course, but usually it'll be 3 inches or more. So figure on having at least 1000 or so pixels on the longest side after cropping.

The photo researcher that Eric works with has requested TIFF files at a minimum of 10MB. That works out to an image that would be around 1870 pixels square. I'm sure they came up with that number to allow for significant cropping.

As another data point, the online stock agency Alamy requires that submitted files be at least 48MB in size. For most digital camera files that will require at least some upsizing (somewhat pointless in my opinion).

So all that said, as long as you attempt to fill the frame or otherwise take your photos in a way that limits cropping, any current 4MP+ digicam at the largest photo setting should provide adequate resolution for most editorial uses. If you really want to have your bases covered (for advertising), go with a 6MP camera. I figure the photos Eric refers to were taken in a smaller format or were cropped significantly.