You can check for the existence of an image by creating a formula field, which looks for the image name in the image library. If found, it will return some HTML, if not it returns nothing, so you're not left with a gap or formatting that you don't want.
For example, this formula will return a single cell table containing the picture, with padding around the image:
string strImg =@"(!IMG_Photo!)";
if(strImg == "" || strImg == null) {
return "";
} else {
return "<table style='padding:0;border-collapse:collapse;border:none;'><td style='padding:5px;'>" + strImg + "</td></table>";
}IMPORTANT NOTE: in the example above, we are referencing another field (an Image field) to get the name of the image. The image field contains HTML Attributes, such as border='0'. Make sure that this attribute does not contain double quotation marks "0" or it will break the formula.